[flashrom] [PATCH]Improve libpayload support, provide libflashrom.a target

[Georgi, Patrick]

Hi,

attached patch contains a couple of build fixes for libpayload builds,
adds a "libpayload" OS_ARCH (which disables serial and usb programmers
and sets up the build to use lpgcc), and provides a new make target
"libflashrom.a" which combines all object files except the CLI_OBJS
class into libflashrom.a.

For a successful build you also need the libpayload patches on the
coreboot mailing list until they're checked in.

libflashrom.a still suffers from a variety of exit(1)s here and there,
so it's not quite a librarified flashrom yet, but it's a start.

Signed-off-by: Patrick Georgi