Most processor modules (e.g., DSP, IVA, IPU) on OMAPs can be reset
under the control of the PRM.  This patch adds an API for this purpose
for OMAP4 devices:

int omap4_prm_is_hardreset_asserted(void __iomem *rstctrl_reg, u8 shift);
int omap4_prm_assert_hardreset(void __iomem *rstctrl_reg, u8 shift);
int omap4_prm_deassert_hardreset(void __iomem *rstctrl_reg, u8 shift);

This API is intended to be used only by the hwmod code - a subsequent
patch will add that support to hwmod.

This patch is a collaboration between Benoît Cousson <b-cousson@ti.com>
and Paul Walmsley <paul@pwsan.com>.
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Benoît Cousson <b-cousson@ti.com>
Tested-by: Kevin Hilman <khilman@deeprootsystems.com>