[ARM] 3829/1: iop3xx: optimise irq entry macros

Squeeze three instructions out of the iop32x irq demuxer, and nine
out of the iop33x irq demuxer by using the hardware vector generator.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>