OMAP2xxx clock: remove implicit dependency between rate CPU flag and clkdev_omap CPU flag

cpu_mask is reused in the OMAP2xxx clock code to match against both the
CPU-specific rate flags (e.g., RATE_IN_2420) and the OMAP clkdev integration
code CPU flags (e.g., CK_242X).  This means that any patch that renumbers the
CK_* macros, as the next patch does, will probably break.  This patch
separates the clkdev_omap and clksel_rate CPU type detection flags so
the CK_* macros can be renumbered freely.

Signed-off-by: Paul Walmsley <paul@pwsan.com>