ARM: OMAP3: McBSP: do not access CM register directly

McBSP driver require special hacks to enable/disable the autoidle feature
for its interface clock for the proper function of the sidetone hardware.
Currently the driver just writes CM registers directly, which should be
avoided. Thus, changed the driver to use the new deny/allow_autoidle
clock API calls.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>