ARM: OMAP2+: omap_device: expose hwmod assert/deassert to omap devices

This API is meant to be an interface to hwmod assert/deassert
function, omap devices can call them through their platform data to
control their reset lines, they are expected to know the name of the
reset line they are trying to control.

Signed-off-by: Omar Ramirez Luna <omar.luna@linaro.org>
[paul@pwsan.com: tweaked some documentation; fixed CodingStyle issue]
Signed-off-by: Paul Walmsley <paul@pwsan.com>