cpu/x86: Use correct config flag for 1GiB page table

The commit below uses USE_1G_PAGETABLES config flag instead of
the correct USE_1G_PAGES_TLB.
"commit ecbc243a45
("cpu/x86: Add 1GiB pages for memory access up to 512GiB")"

Signed-off-by: Bora Guvendik <bora.guvendik@intel.com>
Change-Id: Ic19812bc1f90cbe7d3739c42a0314b3650e0501d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81343
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>

src/cpu/x86/64bit/Makefile.mk

@@ -3,7 +3,7 @@
 all_x86-y += mode_switch.S
 all_x86-y += mode_switch2.S
 
-ifeq ($(CONFIG_USE_1G_PAGETABLES),y)
+ifeq ($(CONFIG_USE_1G_PAGES_TLB),y)
 PAGETABLE_SRC := pt1G.S
 else
 PAGETABLE_SRC := pt.S