[U-Boot] how to get u-boot code with arm64: core support

[TigerLiu at viatech.com.cn]

Hi, bhupesh and drambo:
I think current uboot ARMv8's start.S could handle EL2/EL1 case.
I have tested it on FVP model, let arm trusted firmware boot u-boot.bin.
It seemed ok.
The command I used is:
./Foundation_v8 --cores=4 --no-secure-memory --no-gicv3
--data="./bl1.bin"@0x0 --nsdata="./u-boot.bin"@0x08000000

I changed CONFIG_SYS_TEXT_BASE = 0x0800 0000 (because ARM trusted
firmware will search non-secure firmware entry point at this addr).

Best wishes,