soc/amd/stoneyridge: Enable early cbmem

Add a memmap file with a cbmem_top() function.  Remove the
LATE_CBMEM_INIT, allowing the default of EARLY.  Remove calls
to the late-only set_top_of_ram() function.

Change-Id: I11ad7190031c912642a7312f2fc6f792866288b7
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/19751
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/amd/stoneyridge/Kconfig

@@ -35,7 +35,6 @@ config CPU_SPECIFIC_OPTIONS
 	select HAVE_USBDEBUG_OPTIONS
 	select HAVE_HARD_RESET
 	select LAPIC_MONOTONIC_TIMER
-	select LATE_CBMEM_INIT
 	select SPI_FLASH if HAVE_ACPI_RESUME
 	select TSC_SYNC_LFENCE
 	select SOC_AMD_COMMON

src/soc/amd/stoneyridge/ramtop.c

@@ -15,6 +15,8 @@
 
 #include <stdint.h>
 #include <arch/io.h>
+#include <cpu/x86/msr.h>
+#include <cpu/amd/mtrr.h>
 #include <cbmem.h>
 
 #define CBMEM_TOP_SCRATCHPAD 0x78
@@ -31,3 +33,13 @@ uintptr_t restore_top_of_low_cacheable(void)
 	top_cache = pci_read_config16(PCI_DEV(0,0,0), CBMEM_TOP_SCRATCHPAD);
 	return (top_cache << 16);
 }
+
+void *cbmem_top(void)
+{
+	msr_t tom = rdmsr(TOP_MEM);
+
+	if (!tom.lo)
+		return 0;
+	else
+		return (void *)restore_top_of_low_cacheable();
+}