Add irq domain support for DaVinci cp_intc.

Boot tested on AM18x EVM. Also tested with GPIO IRQ support on
AM18x EVM.
Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: davinci-linux-open-source@linux.davincidsp.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Sergei Shtylyov <sshtylyov@mvista.com>
[nsekhar@ti.com: add commit description, select IRQ_DOMAIN for CP_INTC
in Kconfig]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>