arch/arm: Pass cbmem_top to ramstage via calling argument

This solution is very generic and can in principle be implemented on
all arch/soc.

Instead trying to figure out which files can be removed from stages
and which cbmem_top implementations need with preprocessor, rename all
cbmem_top implementation to cbmem_top_romstage.

Mechanisms set in place to pass on information from rom- to ram-stage
will be placed in a followup commit.

Change-Id: If31f0f1de17ffc92c9397f32b26db25aff4b7cab
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36145
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/cpu/ti/am335x/Makefile.inc

@@ -10,7 +10,6 @@ romstage-y	+= cbmem.c
 ramstage-y	+= dmtimer.c
 ramstage-y	+= monotonic_timer.c
 ramstage-y	+= nand.c
-ramstage-y	+= cbmem.c
 
 bootblock-y	+= uart.c
 romstage-y	+= uart.c