irqchip: pdc: Iterate for actual available pdc regs during hibernation

Current implementation iterates through maximum possible registers
of PDC to save status during hibernation. However some targets have
limited PDC registers available.

Fix this by counting during init time.

Change-Id: I37b048e0edf12cc81efca2087f92c867acb4ed93
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>