arch/x86: Declare GDT symbols and move_gdt()

We relocate GDT to CBMEM, this can be done late in ramstage.
Note: We currently do this for BSP CPU only.

Change-Id: I626faaf22f846433f25ca2253d6a2a5230f50b6b
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7858
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/include/lib.h

@@ -33,9 +33,6 @@ unsigned long log2_ceil(unsigned long x);
 /* Defined in src/lib/lzma.c */
 unsigned long ulzma(unsigned char *src, unsigned char *dst);
 
-/* Defined in src/arch/x86/boot/gdt.c */
-void move_gdt(void);
-
 /* Defined in src/lib/ramtest.c */
 void ram_check(unsigned long start, unsigned long stop);
 int ram_check_nodie(unsigned long start, unsigned long stop);