davinci: dm646x: Adds McASP clock

Adds McASP clock support for the two instances of mcasp (mcasp0,mcasp1). This
patch is part of the audio support for dm646x series.

Signed-off-by: Naresh Medisetty <naresh@ti.com>
Signed-off-by: Chaithrika U S <chaithrika@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>