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Major update to the FVP platform port to use the common platform code
in (include/)plat/arm/* and (include/)plat/common/*. This mainly
consists of removing duplicated code but also introduces some small
behavioural changes where there was unnecessary variation between the
FVP and Juno ports. See earlier commit titled `Add common ARM and CSS
platform code` for details.

Also add support for Foundation FVP version 9.1 during FVP config
setup to prevent a warning being emitted in the console.

Change-Id: I254ca854987642ce09d1b924c9fd410a6e13e3bc