[ARM] pxa: integrate low IRQ chip (ICIP) and high IRQ chip (ICIP2) into one

This makes the code better organized and simplified a bit.  The change
will lose a bit of performance when performing IRQ ack/mask/unmask,but
that's not too much after checking the result binary.

This patch also removes the ugly #ifdef CONFIG_PXA27x .. #endif by
carefully not to access those pxa{27x,3xx} specific registers, this
is done by keeping an internal IRQ number variable.  The pxa-regs.h
is also modified so registers for IRQ > PXA_IRQ(31) are made public
even if CONFIG_PXA{27x,3xx} isn't defined (for pxa25x's sake)

The incorrect assumption in the original code that internal irq starts
from 0 is also corrected by comparing with PXA_IRQ(0).

"struct sys_device" for the IRQ are reduced into one single device on
pxa{27x,3xx}.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>