davinci: Integrate cp_intc support into low-level irq code

Integrate the Common Platform Interrupt Controller (cp_intc)
support into the low-level irq handling for davinci and similar
platforms.  Do it such that support for cp_intc and the original
aintc can coexist in the same kernel binary.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>