x86: add romstage.S to bind program flow and ordering

The build system was previously determining the flow
of the romstage code by the order of files added to
the crt0s make variable. Those files were then
concatenated together, and the resulting file was added
to the build dependencies for romstage proper.

Now romstage.S is added that can be built using
the default object file rules. The generated
romstage.inc is pulled in by way of an #include in the
newly added romstage.S.

TEST=Built vortex, rambi, and some asus boards. compared
     readelf -e output.

Change-Id: Ib1168f9541eaf96651c52d03dc0f60e2489a77bd
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11504
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
2 files changed