x86: Support Intel FSP initialization path in start.S

Per Intel FSP architecture specification, FSP provides 3 routines
for bootloader to call. The first one is the TempRamInit (aka
Cache-As-Ram initialization) and the second one is the FspInit
which does the memory bring up (like MRC for other x86 targets)
and chipset initialization. Those two routines have to be called
before U-Boot jumping to board_init_f in start.S.

The FspInit() will return several memory blocks called Hand Off
Blocks (HOBs) whose format is described in Platform Initialization
(PI) specification (part of the UEFI specication) to the bootloader.
Save this HOB address to the U-Boot global data for later use.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>