ARM: OMAP2+: hwmod: Add support for per hwmod/module context lost count

OMAP4 has module specific context lost registers which makes it now
possible to have module level context loss count, instead of relying
on the powerdomain level context count.

Add 2 private hwmod api's to update/clear the hwmod/module specific
context lost counters/register.

Update the module specific context_lost_counter and clear the hardware
bits just after enabling the module.

omap_hwmod_get_context_loss_count() now returns the hwmod context loss
count them on platforms where they exist (OMAP4), else fall back on
the pwrdm level counters for older platforms.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[paul@pwsan.com: added function kerneldoc, fixed structure kerneldoc,
 rearranged structure to avoid memory waste, marked fns as OMAP4-specific,
 prevent fn entry on non-OMAP4 chips, reduced indentation, merged update
 and clear, merged patches]
[t-kristo@ti.com: added support for arch specific hwmod ops, and changed
 the no context offset indicator to USHRT_MAX]
Signed-off-by: Tero Kristo <t-kristo@ti.com>
[paul@pwsan.com: use NO_CONTEXT_LOSS_BIT flag rather than USHRT_MAX;
 convert unsigned context lost counter to int to match the return type;
 get rid of hwmod_ops in favor of the existing soc_ops mechanism;
 move context loss low-level accesses to the PRM code]
Signed-off-by: Paul Walmsley <paul@pwsan.com>