powerpc/p1022ds: fix broken mpic timer node

There is no hardware interrupt 0xf7.  But now we can express the timer
interrupt using 4-cell interrupts.  This requires converting all of the
other interrupt specifiers in the tree as well.

Also add the second timer group, and fix the reg property to only
describe the timer registers.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>