Emit warnings when using deprecated GIC init

Emit runtime warnings when intializing the GIC drivers using the
deprecated method of defining integer interrupt arrays in the GIC driver
data structures; interrupt_prop_t arrays should be used instead. This
helps platforms detect that they have migration work to do. Previously,
no warning was emitted in this case. This affects both the GICv2 and GICv3
drivers.

Also use the __deprecated attribute to emit a build time warning if these
deprecated fields are used. These warnings are suppressed in the GIC
driver compatibility functions but will be visible if platforms use them.

Change-Id: I6b6b8f6c3b4920c448b6dcb82fc18442cfdf6c7a
Signed-off-by: Dan Handley <dan.handley@arm.com>