OMAP3 clock: Add capability to change rate of dpll4_m5_ck

Add necessary definitions to clock framework to allow changing
dpll4_m5_ck rate.  This is used by the camera code.

Signed-off-by: Jouni Högander <jouni.hogander@nokia.com>
Signed-off-by: Tuukka Toivonen <tuukka.o.toivonen@nokia.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>