cpu/x86: add paging_set_default_pat() function

Add paging_set_default_pat() which sets up the PAT MSR according
to util/x86/x86_page_tables.go. Using page attribute types require
a matching of the PAT values with the page table entries. This function
is just providing the default PAT MSR value to match against the
utility.

BUG=b:72728953

Change-Id: I7ed34a3565647ffc359ff102d3f6a59fbc93cc22
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25715
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Justin TerAvest <teravest@chromium.org>

src/include/cpu/x86/pae.h

@@ -14,8 +14,18 @@ void paging_disable_pae(void);
 /* Set/Clear NXE bit in IA32_EFER MSR */
 void paging_set_nxe(int enable);
 
+#define PAT_UC		0
+#define PAT_WC		1
+#define PAT_WT		4
+#define PAT_WP		5
+#define PAT_WB		6
+#define PAT_UC_MINUS	7
+#define PAT_ENCODE(type, idx) (((uint64_t)PAT_ ## type) << 8*(idx))
+
 /* Set PAT MSR */
 void paging_set_pat(uint64_t pat);
+/* Set coreboot default PAT value. */
+void paging_set_default_pat(void);
 
 #define MAPPING_ERROR ((void *)0xffffffffUL)
 void *map_2M_page(unsigned long page);