OMAP2/3: PRCM: split OMAP2/3-specific PRCM code into OMAP2/3-specific files

In preparation for adding OMAP4-specific PRCM accessor/mutator
functions, split the existing OMAP2/3 PRCM code into OMAP2/3-specific
files.  Most of what was in mach-omap2/{cm,prm}.{c,h} has now been
moved into mach-omap2/{cm,prm}2xxx_3xxx.{c,h}, since it was
OMAP2xxx/3xxx-specific.

This process also requires the #includes in each of these files to be
changed to reference the new file name.  As part of doing so, add some
comments into plat-omap/sram.c and plat-omap/mcbsp.c, which use
"sideways includes", to indicate that these users of the PRM/CM includes
should not be doing so.

Thanks to Felipe Contreras <felipe.contreras@gmail.com> for comments on this
patch.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Jarkko Nikula <jhnikula@gmail.com>
Cc: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: Omar Ramirez Luna <omar.ramirez@ti.com>
Acked-by: Omar Ramirez Luna <omar.ramirez@ti.com>
Cc: Felipe Contreras <felipe.contreras@gmail.com>
Acked-by: Felipe Contreras <felipe.contreras@gmail.com>
Cc: Greg Kroah-Hartman <greg@kroah.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Kevin Hilman <khilman@deeprootsystems.com>
Tested-by: Kevin Hilman <khilman@deeprootsystems.com>
Tested-by: Rajendra Nayak <rnayak@ti.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>