OMAP2/3: PRM/CM: prefix OMAP2 PRM/CM functions with "omap2_"

Now that OMAP4-specific PRCM functions have been added, distinguish the
existing OMAP2/3-specific PRCM functions by prefixing them with "omap2_".

This patch should not result in any functional change.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Jarkko Nikula <jhnikula@gmail.com>
Cc: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Rajendra Nayak <rnayak@ti.com>