net: ravb: Support multiple clocks

The RZ/G2 series uses an external clock as a reference to the AVB.
If this clock is controlled by an external programmable clock,
it must be requested by the consumer or it will not turn on.
In order to do this, update the driver to use bulk enable and
disable functions to enable clocks for boards with multiple clocks.

Signed-off-by: Adam Ford <aford173@gmail.com>