[POWERPC] Add arch/powerpc driver for UIC, PPC4xx interrupt controller

This patch adds a driver to arch/powerpc/sysdev for the UIC, the
on-chip interrupt controller from IBM/AMCC 4xx chips.  It uses the new
irq host mapping infrastructure.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>