AMD (K8/fam10): Rewrite CAR migration in post_cache_as_ram

Old routine copied all of CAR region as-is right below CONFIG_RAMTOP.
Most of this region was reserved to interleave AP CPU address spaces
and unused on BSP CPU. The only part of CAR region requiring a copy
in RAM is the sysinfo structure.

Improved routine changes this as follows:

A region of size 'backup_size' below CONFIG_RAMTOP is cleared. In
case of S3 resume, OS context from this region is first copied to
high memory (CBMEM_ID_RESUME).

At stack switch, CAR stack is discarded. Top of the stack for BSP
is located at 'CONFIG_RAMTOP - car_size' for the remaining part
of the romstage. This region is part of 'backup_size' and was zeroed
before the switch took place.

Before CAR is torn down the region of CAR_GLOBALS (and CAR_CBMEM),
including the relevant sysinfo data for AP nodes memory training,
is copied at 'CONFIG_RAMTOP - car_size'.

NOTE: While CAR_GLOBAL variables are recovered, there are currently
no means to calculate their offsets in RAM.

NOTE: Boards with multiple CPU packages are likely already broken since

  bbc880ee amdk8/amdfam10: Use CAR_GLOBAL for sysinfo

This moved the copy of sysinfo in RAM from above the stack to below
the stack, but code for AP CPU's was not adjusted accordingly.

Change-Id: Ie45b576aec6a2e006bfcb26b52fdb77c24f72e3b
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/4583
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/include/cpu/amd/car.h

@@ -5,8 +5,8 @@ void cache_as_ram_main(unsigned long bist, unsigned long cpu_init_detectedx);
 void done_cache_as_ram_main(void);
 void post_cache_as_ram(void);
 
-void cache_as_ram_switch_stack(void *resume_backup_memory);
-void cache_as_ram_new_stack(void *resume_backup_memory);
+void cache_as_ram_switch_stack(void *stacktop);
+void cache_as_ram_new_stack(void);
 
 #if CONFIG_CPU_AMD_AGESA
 void disable_cache_as_ram(void);