OMAP: hwmod: add an hardreset API for use by other core code

Expose an hardreset API from hwmod in order to assert / deassert all the
individual reset lines that belong to an hwmod.  This API is needed by
some of the more complicated processor drivers, e.g., DSP/Bridge,
Syslink, etc.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>