cpu/intel/socket_BGA956: Double DCACHE_RAM_SIZE to 64 kB

This fixes building lenovo/x200 with VBOOT.
All supported CPUs have enough L2 cache to support this.

Change-Id: Ifd6a16ce36c86349955cd7b7ddb3f74a19c17c4d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71905
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/cpu/intel/socket_BGA956/Kconfig

@@ -10,7 +10,7 @@ config DCACHE_RAM_BASE
 
 config DCACHE_RAM_SIZE
 	hex
-	default 0x8000
+	default 0x10000
 
 config DCACHE_BSP_STACK_SIZE
 	hex