clk: meson: g12a: expose CPUB clock ID for G12B

Expose the CPUB clock id to add DVFS to the second CPU cluster of
the Amlogic G12B SoC.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>