amd/stoneyridge: Add NV storage to ramtop

The scratch registers in northbridge used for storing the top of
cacheable memory are volatile.  Use the BiosRam storage in the FCH
instead.

TEST=Suspend and resume Kahlee with complete S3 patch stack
BUG=b:69614064

Change-Id: Ieb3cfd173c70bf899a6391d62d1df87b38485f30
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/22726
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/amd/stoneyridge/Makefile.inc

@@ -47,6 +47,7 @@ bootblock-y += reset.c
 bootblock-y += sb_util.c
 bootblock-y += tsc_freq.c
 bootblock-y += southbridge.c
+bootblock-y += sb_util.c
 
 romstage-y += BiosCallOuts.c
 romstage-y += i2c.c
@@ -76,6 +77,7 @@ verstage-y += tsc_freq.c
 postcar-y += monotonic_timer.c
 postcar-$(CONFIG_STONEYRIDGE_UART) += uart.c
 postcar-y += ramtop.c
+postcar-y += sb_util.c
 
 ramstage-y += BiosCallOuts.c
 ramstage-y += i2c.c

src/soc/amd/stoneyridge/include/soc/iomap.h

@@ -66,4 +66,7 @@
 #define AMD_GPIO_MUX			(AMD_SB_ACPI_MMIO_ADDR + 0x00000d00)
 #define AMD_GPIO_CONTROL		(AMD_SB_ACPI_MMIO_ADDR + 0x00001500)
 
+/* BiosRam Ranges at 0xfed80500 or I/O 0xcd4/0xcd5 */
+#define BIOSRAM_CBMEM_TOP		0xf0 /* 4 bytes */
+
 #endif /* __SOC_STONEYRIDGE_IOMAP_H__ */

src/soc/amd/stoneyridge/ramtop.c

@@ -22,20 +22,16 @@
 #include <cpu/amd/mtrr.h>
 #include <cbmem.h>
 #include <soc/northbridge.h>
-
+#include <soc/southbridge.h>
-#define CBMEM_TOP_SCRATCHPAD 0x78
 
 void backup_top_of_low_cacheable(uintptr_t ramtop)
 {
-	uint16_t top_cache = ramtop >> 16;
+	biosram_write32(BIOSRAM_CBMEM_TOP, ramtop);
-	pci_write_config16(PCI_DEV(0,0,0), CBMEM_TOP_SCRATCHPAD, top_cache);
 }
 
 uintptr_t restore_top_of_low_cacheable(void)
 {
-	uint16_t top_cache;
+	return biosram_read32(BIOSRAM_CBMEM_TOP);
-	top_cache = pci_read_config16(PCI_DEV(0,0,0), CBMEM_TOP_SCRATCHPAD);
-	return (top_cache << 16);
 }
 
 void *cbmem_top(void)