clk: meson: meson8b: add the vclk_en gate clock

HHI_VID_CLK_CNTL[19] is documented as CLK_EN0. This description is the
same in the public S912 datasheet and the GXBB driver calls this gate
"vclk". Add this gate clock to the Meson8/Meson8b/Meson8m2 clock
controller because it's needed to make the video output work.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200629203904.2989007-2-martin.blumenstingl@googlemail.com