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Adds bl2 with FIP to the build required for mbed Linux booting where
we do:

BootROM -> SPL -> BL2 -> OPTEE -> u-boot

If NEED_BL2 is specified then BL2 will be built and BL31 will have
its address range modified upwards to accommodate. BL31 must be
loaded from a FIP in this case.

If NEED_BL2 is not specified then the current BL31 boot flow is
unaffected and u-boot SPL will load and execute BL31 directly.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Change-Id: I655343b3b689b1fc57cfbedda4d3dc2fbd549a96