GIC-Clayton supports multichip operation mode which allows it to connect
upto 16 other GIC-Clayton instances. GIC-Clayton's multichip programming
and operation remains same as GIC-600 with a minor change in the
SPI_BLOCKS and SPI_BLOCK_MIN shifts to accommodate additional SPI
ranges. So identify if the GIC v4 extension is enabled by the platform
makefile and appropriately select the SPI_BLOCKS and SPI_BLOCK_MIN
shifts.

Change-Id: I95fd80ef16af6c7ca09e2335539187b133052d41
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>