x86_64 EFI boot support: EFI boot document

This patch adds document for EFI x86_64 boot support.  The setup and operation
guide of EFI based system is documented in Documentation/x86_64/uefi.txt.
Signed-off-by: NChandramouli Narayanan <mouli@linux.intel.com>
Signed-off-by: NHuang Ying <ying.huang@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/x86_64/uefi.txt

+General note on [U]EFI x86_64 support
+-------------------------------------
+
+The nomenclature EFI and UEFI are used interchangeably in this document.
+
+Although the tools below are _not_ needed for building the kernel,
+the needed bootloader support and associated tools for x86_64 platforms
+with EFI firmware and specifications are listed below.
+
+1. UEFI specification:  http://www.uefi.org
+
+2. Booting Linux kernel on UEFI x86_64 platform requires bootloader
+   support. Elilo with x86_64 support can be used.
+
+3. x86_64 platform with EFI/UEFI firmware.
+
+Mechanics:
+---------
+- Build the kernel with the following configuration.
+	CONFIG_FB_EFI=y
+	CONFIG_FRAMEBUFFER_CONSOLE=y
+- Create a VFAT partition on the disk
+- Copy the following to the VFAT partition:
+	elilo bootloader with x86_64 support, elilo configuration file,
+	kernel image built in first step and corresponding
+	initrd. Instructions on building elilo	and its dependencies
+	can be found in the elilo sourceforge project.
+- Boot to EFI shell and invoke elilo choosing the kernel image built
+  in first step.