OMAP3 clock: split out DPLL3 M2 divider functions into mach-omap2/clkt34xx_dpll3m2.c

OMAP3 clock: split out DPLL3 M2 divider functions into mach-omap2/clkt34xx_dpll3m2.c

Split the DPLL3 M2 divider clock functions out of clock34xx.c and move
them into mach-omap2/clkt34xx_dpll3m2.c. This is intended to make the
clock code easier to understand, since all of the functions needed to
manage the OMAP3 DPLL3 M2 divider are now located in their own file,
rather than being mixed with other, unrelated functions.

Clock debugging is also now more finely-grained, since the DEBUG macro
can now be defined for the DPLL3 M2 clock alone.  This should reduce
unnecessary console noise when debugging DVFS.

Also, if at some future point the mach-omap2/ directory is split
into OMAP2/3/4 variants, this clkt file can be placed in the mach-omap34xx/
directory, rather than shared with other chip types that don't use this
clock type.

This patch also lays the groundwork to skip compilation of this
code on OMAP3 chips that don't support DVFS (e.g., AM35xx) via
the Makefile, rather than via #ifdefs.

Thanks to Alexander Shishkin <virtuoso@slind.org> for his comments to
improve the patch description.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Jouni Högander <jouni.hogander@nokia.com>
Cc: Alexander Shishkin <virtuoso@slind.org>