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>

Add support to configure GIC-600's multichip routing table registers.
Introduce a new gic600 multichip structure in order to support platforms
to pass their GIC-600 multichip information such as routing table owner,
SPI blocks ownership.

This driver is currently experimental and the driver api may change in
the future.

Change-Id: Id409d0bc07843e271ead3fc2f6e3cb38b317878d
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>