plat/arm: Check the need for firmware update only once
plat/arm: Check the need for firmware update only once

Currently, the need for firmware update is being checked twice
in the code hence modifications are done to do this check only
once and set the global variable.
Then this global variable helps to decide whether to go for
normal boot or firmware update flow.

Change-Id: I8469284555a8039786f34670f9dc4830f87aecc1
Signed-off-by: Manish V Badarkhe <d2342ad575f6bc1a5f5a5b89d6db0f72dd7e0e4c@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware