This is something of an ugly hack to accommodate an OEM requirement.
The NIC has only one expansion ROM BAR, rather than one per port.  To
allow individual ports to be selectively enabled/disabled for PXE boot
(as required), we must therefore leave the expansion ROM always
enabled, and place the per-port enable/disable logic within the gPXE
driver.

The Phantom firmware selectively disables PCI functions based on the
board type, with the end result that we see one PCI function for each
network port.  This allows us to eliminate the code for reading from
flash and, more importantly, removes knowledge of the board type magic
number from the gPXE driver.

Settings can be constructed using a dotted-decimal notation, to allow
for access to unnamed settings.  The default interpretation is as a
DHCP option number (with encapsulated options represented as
"<encapsulating option>.<encapsulated option>".

In several contexts (e.g. SMBIOS, Phantom CLP), it is useful to
interpret the dotted-decimal notation as referring to non-DHCP
options.  In this case, it becomes necessary for these contexts to
ignore standard DHCP options, otherwise we end up trying to, for
example, retrieve the boot filename from SMBIOS.

Allow settings blocks to specify a "tag magic".  When dotted-decimal
notation is used to construct a setting, the tag magic value of the
originating settings block will be ORed in to the tag number.
Store/fetch methods can then check for the magic number before
interpreting arbitrarily-numbered settings.

This interface provides access to firmware settings (e.g. MAC address)
that will apply to all drivers loaded for the duration of the current
system boot.

A hardware bug means that reads through the expansion ROM BAR can
return corrupted data if the PEGs are running.  This breaks platforms
that re-read the expansion ROM after invoking gPXE code, such as IBM
blade servers.

Halt PEGs during driver shutdown, and unhalt PEGs during driver
startup if we detect that this is not the first startup since
power-on.

The Phantom firmware debug logs can be extremely long, so add the
ability to restrict the output to the last N lines.

Most other Phantom drivers define a register space in terms of a 64M
virtual address space.  While this doesn't map in any meaningful way
to the actual addresses used on the latest cards, it makes maintenance
easier if we do the same.

It is possible for the BIOS to use the UNDI API to bring up the NIC
prior to system boot.  If this happens, UNM_NIC_REG_CMDPEG_STATE will
contain the value 0xf00f (UNM_NIC_REG_CMDPEG_STATE_INITIALIZE_ACK),
and we should skip initialising the command PEG.

The firmware will now determine the right port mode on all cards, so
the PXE driver doesn't have to set it.  (Setting the port mode
apparently breaks some newer cards.)

Commit f58cc3f introduced a temporary workaround for a bug in current
prototype silicon, but failed to apply it to all eight PCI functions
within the device.

Conjecture: The hardware issues 64-bit DMA writes of status descriptors,
which some PCI bridges seem to split into two 32-bit writes in reverse
order (i.e. dword 1 first).  This means that we sometimes observe a
partial status descriptor.  Add an explicit check to ensure that the
descriptor is complete before processing it.

Also ensure that the RDS consumer counter is incremented only when we
know that we have actually consumed an RX descriptor.