spl: add support to booting with ATF

spl: add support to booting with ATF

ATF(ARM Trusted Firmware) is used by ARM arch64 SoCs, find more infomation
about ATF at: https://github.com/ARM-software/arm-trusted-firmware

SPL is considered as BL2 in ATF terminology, it needs to load other parts
of ATF binary like BL31, BL32, SCP-BL30, and BL33(U-Boot). And needs to
prepare the parameter for BL31 which including entry and image information
for all other images. Then the SPL handle PC to BL31 with the parameter,
the BL31 will do the rest of work and at last get into U-Boot(BL33).

This patch needs work with patches from Andre for SPL support multi
binary in FIT.

The entry point of bl31 and bl33 are still using hard code because we
still can not get them from the FIT image information.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>