EFI_PCI_DEVICE_ENABLE is a list of the standard attributes that must
be enabled for a PCI device to function: I/O cycles, memory cycles,
and bus-mastering.  We currently call EFI_PCI_IO_PROTOCOL::Attribute()
with the parameter EFI_PCI_DEVICE_ENABLE to enable a PCI device.  This
should translate to a single write to PCI configuration space.

Simplicity is not a virtue within the UEFI world.  Some platforms will
'helpfully' report an error if EFI_PCI_DEVICE_ENABLE is used on a
device that doesn't actually support all three of the relevant
attributes.  For example, if a PCI device provides only memory-mapped
accesses (and so hardwires the I/O enable bit to zero), then using
EFI_PCI_DEVICE_ENABLE on such a platform will result in an
EFI_UNSUPPORTED error.

There is no plausible use case in which it is useful for the platform
to return an error in this way, and doing so makes it impossible to
distinguish genuine errors from noise.

Work around this broken behaviour by attempting to enable the three
attributes individually, and ignoring any errors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>