armv7: add a wrapper for romstage's main() for ARM ISA

This adds a wrapper around main() in romstage which is compiled using
-marm. This assumes that the bootblock branches to romstage in ARM
mode.

The long-term idea is to enforce ABI compatibility when handing off to
the next stage by using shims which are which are compiled in a pre-
determiend manner and leave the main portions of each stage up to
whatever the compiler wants. So it will eventually look like this:
1. bootblock_main (ARM/Thumb)
2. bootblock_exit (ARM)
3. romstage_entry (ARM)
4. romstage_main (ARM/Thumb)

(credit to Gabe Black for writing the patch, I'm just uploading it)

Change-Id: I4fdb8d2c6c2c0a7178bcb9154c378ddce0567309
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Signed-off-by: Gabe Black <gabeblack@chromium.org>
Reviewed-on: http://review.coreboot.org/2175
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
4 files changed