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.

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.

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