Several SPI chips will respond to an SPI read command with a dummy
zero bit immediately prior to the first real data bit.  This can be
used to autodetect the address length, provided that the command
length and data length are already known, and that the MISO data line
is tied high.

Tested-by: Thomas Miletich <thomas.miletich@gmail.com>
Debugged-by: Thomas Miletich <thomas.miletich@gmail.com>

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Some devices (e.g. the Atmel AT24C11) have no concept of a device
address; they respond to every device address and use this value as
the word address.  Some other devices use part of the device address
field to extend the word address field.

Generalise the i2c bit-bashing support to handle this by defining the
device address length and word address length as properties of an i2c
device.  The word address is assumed to overflow into the device
address field if the address used exceeds the width of the word
address field.

Also add a bus reset mechanism.  i2c chips don't usually have a reset
line, so rebooting the host will not clear any bizarre state that the
chip may be in.  We reset the bus by clocking SCL until we see SDA
high, at which point we know we can generate a start condition and
have it seen by all devices.  We then generate a stop condition to
leave the bus in a known state prior to use.

Finally, add some extra debugging messages to i2c_bit.c.

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>

(i.e. LSB transmitted first on the wire), even though SPI commands and
addresses always have to be big-endian.

device.

Separated the mechanisms of non-volatile storage access and non-volatile
stored options.

a word length.

that don't provide the full flexibility of a bit-bashing interface.

Temporarily hacked rtl8139.c to use the new interface.

defined in vsprintf.h.  (This may change, since vsprintf.h is a
non-standard name, but for now it's the one to use.)

There should be no need to include vsprintf.h just for DBG() statements,
since include/compiler.h forces it in for a debug build anyway.

Update rtl8139 driver to instantiate an SPI interface with a three-wire
device attached.

(since SPI bit-bashing will require different delay semantics).