ARM: OMAP2+: hwmod: use init-time function pointer for hardreset

Rather than using cpu_is* checking at runtime, initialize SoC specific
function pointers for the various hard reset functions at init time.

Signed-off-by: Kevin Hilman <khilman@ti.com>
[paul@pwsan.com: convert to use soc_ops function pointers; add kerneldoc]
Signed-off-by: Paul Walmsley <paul@pwsan.com>