OMAP4: hwmod data: Add PRM context register offset

Add a 'context_offs' entry in the prcm.omap4 structure to all
IPs when applicable.
The offset will be used to retrieve the per module context lost
information now available on OMAP4.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>