m68knommu: modify clock code so it can be used by all ColdFire CPU types

The existing clk.c code for ColdFire CPUs has one set of functions to
support those CPU types that have selectable clocks (those with a PPMCR
register), and a duplicate simpler set for those with static clocks.

Modify the clk.c code so there is just one set of support functions. All
CPU types now define a list of clocks (in "struct clk"s), so we only need
a single set of clock functions.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>