The current IRQ domain implementation in the VIC allocates 32
interrupts for each VIC instance no matter whether the
controller actually use all the IRQs or not. Alter this so
we only allocate a domain up until the last IRQ marked valid.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>