UPSTREAM: AGESA: Move romstage main entry under cpu

As we now apply asmlinkage attributes to romstage_main()
entry, also x86_64 passes parameters on the stack.

BUG=none
BRANCH=none
TEST=none

Change-Id: Idc959f24a256aa5c77b00b030b2d01b0ea6dd127
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: df7ff31c59
Original-Change-Id: If9938dbbe9a164c9c1029431499b51ffccb459c1
Original-Signed-off-by: Kysti Mlkki <kyosti.malkki@gmail.com>
Original-Reviewed-on: https://review.coreboot.org/18624
Original-Tested-by: build bot (Jenkins)
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/471448

src/include/cpu/amd/car.h

@@ -18,4 +18,6 @@ void disable_cache_as_ram(void);
 
 void asmlinkage early_all_cores(void);
 
+void * asmlinkage romstage_main(unsigned long bist);
+
 #endif