The Allwinner sun55i (A523/A527/T527) platform requires the MBUS clock
gate enabled for the gmac1 controller to function. Add the clock gate
definition for CLK_MBUS_EMAC1.
Signed-off-by: Junhui Liu <junhui.liu@pigmoral.tech> Reviewed-by: Andre Przywara <andre.przywara@arm.com>