arch: use Kconfig variable for coreboot table size

Instead of hard coding a #define in each architecture's
tables.c for the coreboot table size in cbmem use a Kconfig
varible. This aids in aligning on a common write_tables()
implementation instead of duplicating the code for each
architecture.

Change-Id: I09c0f56133606ea62e9a9c4c6b9828bc24dcc668
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14429
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/Kconfig

@@ -658,6 +658,15 @@ config ACPI_NHLT
 	help
 	  Build support for NHLT (non HD Audio) ACPI table generation.
 
+
+config COREBOOT_TABLE_SIZE
+	hex
+	default 0x8000 if ARCH_X86
+	default 0x2000 if !ARCH_X86
+	help
+	  The amount of memory to reserve for the coreboot tables in
+	  cbmem.
+
 #These Options are here to avoid "undefined" warnings.
 #The actual selection and help texts are in the following menu.