armv7: unify stage hand-off routines

This replaces the current stage-specific exit/entry functions with
generic versions. Now all stages compile with stage_entry(), which
is placed at .text.stage_entry.armv7, and stage_exit().

Snow's ramstage files are also updated to avoid build breakage.

Change-Id: I953a2c4b8121bd4b66c3362557997a9ca3aa53b0
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2254
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
11 files changed