add transforms

Transforms transform coreboot ROM images to add or remove capabilities.
They let us test out new ideas for coreboot while not impacting
the coreboot source in any way.

So, for example, should we want an image with a rampayload, we can
run the normal build process and then transform the resulting rom image
as needed.

We can implement a postcar stage which loads a ram payload directly,
and do so in a way which has no impact on the coreboot source.

This not only lets us change the output of the build process, it can be implemented
without changing the coreboot source. Further, since the transform Makefile depends
on the presence of a coreboot.rom in the directory, we can avoid the build step
if we're just trying to transform a ROM we read from a FLASH part. Just flashrom
-r the image, drop it into coreboot.rom in this directory, and no build
will be attempted.

This example represents the first steps of building a rampayload transform.

Transforms should have zero impact on the $(top)/src tree, since they
are intended to be able to be used on prebuilt images. I did have to make
one thing user selectable, namely, NO_RELOCATABLE_RAMSTAGE.

If you do not select NO_RELOCATABLE_RAMSTAGE,
the payloader works as a payload but fails as a stage with
the cryptic message:
CBFS: Locating 'fallback/postcar'
CBFS: Found @ offset 14bc0 size 1008c
Decompressing stage fallback/postcar @ 0x07f85fc0 (349968 bytes)
Failed to load after CAR program.

There is a bit more work to figuring out how to make it an rmod.

To test this:
build a qemu-q35 image, select the payloader payload, select
NO_RELOCATABLE_RAMSTAGE
in whatever manner you prefer. Make. To test:
/usr/bin/qemu-system-x86_64 -M q35 -bios build/coreboot.rom -serial /dev/tty -nographic

when this  runs you will see
.
.
.
BS: BS_PAYLOAD_LOAD times (ms): entry 0 run 12 exit 0
Jumping to boot code at 00100000(07fcb000)
payload loaded at 0x111830
Greetings from the payloader, which loads payloads.
Now we will halt. Bye

now cd transforms/rampayload, and
make run

You should see the same output.

Change-Id: I27c5686000f79e287adce3f0fa7b608683a9bfce
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
---
M payloads/Kconfig
M payloads/Makefile.inc
A payloads/payloader/Makefile
A payloads/payloader/i386.c
A payloads/payloader/payloader.c
A payloads/payloader/payloader.h
M src/Kconfig
A transforms/README
A transforms/rampayload/Makefile
9 files changed, 210 insertions(+), 3 deletions(-)