ARM: OMAP3: pm: use prcm chain handler

PM interrupt handling is now done through the PRCM chain handler. The
interrupt handling logic is also split in two parts, to serve IO and
WKUP events separately. This allows us to handle IO chain events in a
clean way.

Core event code is also changed in accordance to this, as PRCM
interrupt handling is done by independent handlers, and the core
handler should not clear the IO events anymore.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
[paul@pwsan.com: use pr_err(); combined with portions of earlier patches and
 the "do not enable PRCM MPU interrupts manually" patch]
Signed-off-by: Paul Walmsley <paul@pwsan.com>