[ARM] VIC: Add power management device

Add power management support to the VIC by registering
each VIC as a system device to get suspend/resume
events going.

Since the VIC registeration is done early, we need to
record the VICs in a static array which is used to add
the system devices later once the initcalls are run. This
means there is now a configuration value for the number
of VICs in the system.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>