OMAP2430/3xxx: clock: add modem clock autoidle support

OMAP2430 and OMAP3xxx have modem autoidle bits that are actually
attached to clocks with CM_FCLKEN bits; add the code and data to
handle these.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Rajendra Nayak <rnayak@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>