cpu/amd: Correct number of MCA banks cleared

Use the value discovered in the MCG_CAP[Count] for the number of MCA
status registers to clear.  The generations should have the following
number of banks:
 * Family 10h: 6 banks
 * Family 12h: 6
 * Family 14h: 6
 * Family 15h: 7
 * Family 16h: 6

Change-Id: I0fc6d127a200b10fd484e051d84353cc61b27a41
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/27923
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>

src/include/cpu/amd/amdfam15.h

@@ -16,6 +16,8 @@
 #ifndef CPU_AMD_FAM15_H
 #define CPU_AMD_FAM15_H
 
+#define MCG_CAP				0x00000179
+# define MCA_BANKS_MASK			0xff
 #define MC0_STATUS			0x00000401
 #define MSR_SMM_BASE			0xC0010111
 #define MSR_TSEG_BASE			0xC0010112

src/include/cpu/amd/amdfam16.h

@@ -16,6 +16,8 @@
 #ifndef CPU_AMD_FAM16_H
 #define CPU_AMD_FAM16_H
 
+#define MCG_CAP				0x00000179
+# define MCA_BANKS_MASK			0xff
 #define MC0_STATUS			0x00000401
 #define HWCR_MSR			0xC0010015
 #define NB_CFG_MSR			0xC001001f