clk: mediatek: add support for gate ID at offset

clk: mediatek: add support for gate ID at offset

Add support to clk_gate ops to reference the clk ID at an offset by
using the just introduced gates_offs value from the unified muxes +
gates implementation.

Gate clock that doesn't have gates_offs set won't be affected as the
offset will simply be 0 and won't be offset of any value.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>