[coreboot] removing bounce buffers

[ron minnich]

we are at long last removing bounce buffers from selfboot.
https://review.coreboot.org/c/coreboot/+/28647

This greatly simplifies the code and there are almost no platforms left
that need them. Here are the ones that seem to:

src/northbridge/amd/amdfam10/Kconfig
src/northbridge/amd/lx/Kconfig
src/northbridge/via/vx900/Kconfig
src/soc/intel/fsp_baytrail/Kconfig
src/soc/intel/fsp_broadwell_de/Kconfig

For these boards, I made the following change:
"For these five boards we change CONFIG_RAMBASE from 0x100000 (the
value needed in 1999 for the 32-bit Linux kernel, the original ramstage)
to 0x3d00000 (64 MiB - 2 MiB) which will put the non-relocatable x86
ramstage out of the way of any reasonable payload until we can
get rid of it for good."

Julius suggested that I ping the list to see if anyone would like to test
with the change.
The change is +2'ed but i will wait to submit it for another day or so.

thanks
ron