bl2-el3: Add BL2 at EL3 support in FVP

bl2-el3: Add BL2 at EL3 support in FVP

This patch add supports for the new API added for BL2 at EL3 for
FVP. We don't have a non-TF Boot ROM for FVP, but this option can be
tested setting specific parameters in the model.

The bl2 image is loaded directly in memory instead of being loaded
by a non-TF Boot ROM and the reset address is changed:

	--data cluster0.cpu0=bl2.bin@0x4001000
	-C cluster0.cpu0.RVBAR=0x4001000

These parameters mean that in the cold boot path the processor will
jump to BL2 again. For this reason, BL2 is loaded in dram in this
case, to avoid other images reclaiming BL2 memory.

Change-Id: Ieb2ff8535a9e67ccebcd8c2212cad366e7776422
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>