x86: Add support for starting 64-bit kernel

Add code to jump to a 64-bit Linux kernel. We need to set up a flat page
table structure, a new GDT and then go through a few hoops in the right
order.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/Makefile b/arch/x86/cpu/Makefile
index e7bb3e3..9d38ef7 100644
--- a/arch/x86/cpu/Makefile
+++ b/arch/x86/cpu/Makefile
@@ -10,4 +10,4 @@
 
 extra-y	= start.o
 obj-$(CONFIG_X86_RESET_VECTOR) += resetvec.o start16.o
-obj-y	+= interrupts.o cpu.o
+obj-y	+= interrupts.o cpu.o call64.o