arch/x86 & commonlib: Add macros for postcodes used in x86/tables

The 0x9a, 0x9b, and 0x9c postcodes are not used anywhere else in the
coreboot tree other than in arch/x86/tables.c.  Add macros to
standardize these postcodes.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I16be65ffa3f0b253fe4a9bb7bfb97597a760ad3f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69200
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
diff --git a/src/arch/x86/tables.c b/src/arch/x86/tables.c
index 5940c64..b4b97b4 100644
--- a/src/arch/x86/tables.c
+++ b/src/arch/x86/tables.c
@@ -17,7 +17,7 @@
 	unsigned long high_table_pointer;
 
 #define MAX_PIRQ_TABLE_SIZE (4 * 1024)
-	post_code(0x9a);
+	post_code(POST_X86_WRITE_PIRQ_TABLE);
 
 	/* This table must be between 0x0f0000 and 0x100000 */
 	rom_table_end = write_pirq_routing_table(rom_table_end);
@@ -49,7 +49,7 @@
 	unsigned long high_table_pointer;
 
 #define MAX_MP_TABLE_SIZE (4 * 1024)
-	post_code(0x9b);
+	post_code(POST_X86_WRITE_MPTABLE);
 
 	/* The smp table must be in 0-1K, 639K-640K, or 960K-1M */
 	rom_table_end = write_smp_table(rom_table_end);
@@ -78,7 +78,7 @@
 	unsigned long high_table_pointer;
 	const size_t max_acpi_size = CONFIG_MAX_ACPI_TABLE_SIZE_KB * KiB;
 
-	post_code(0x9c);
+	post_code(POST_X86_WRITE_ACPITABLE);
 
 	/* Write ACPI tables to F segment and high tables area */