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/cpu/x86/mp_init.c

@@ -26,6 +26,7 @@
 #include <cpu/cpu.h>
 #include <cpu/intel/microcode.h>
 #include <cpu/x86/cache.h>
+#include <cpu/x86/gdt.h>
 #include <cpu/x86/lapic.h>
 #include <cpu/x86/name.h>
 #include <cpu/x86/msr.h>
@@ -67,10 +68,6 @@ struct saved_msr {
 
 /* The sipi vector rmodule is included in the ramstage using 'objdump -B'. */
 extern char _binary_sipi_vector_start[];
-/* These symbols are defined in c_start.S. */
-extern char gdt[];
-extern char gdt_end[];
-extern char idtarg[];
 
 /* The SIPI vector is loaded at the SMM_DEFAULT_BASE. The reason is at the
  * memory range is already reserved so the OS cannot use it. That region is