ARM: AM43XX: Add functions to enable and disable EDMA3 clocks

Adds functions to enable and disable edma3 clocks which can be invoked
by drivers using edma3 to control the clocks.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>