ARM: OMAP2+: hwmod: add support for lock and unlock hooks

Some IP blocks like RTC, needs an additional setting for writing to its
registers. This is to prevent any spurious writes from changing the
register values.

This patch adds optional lock and unlock function pointers to
the IP block's hwmod data. These unlock and lock function pointers
are called by hwmod code before and after writing sysconfig registers.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[paul@pwsan.com: fixed indentation level to conform with the rest of the
 structure members]
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>