pwm: meson: don't use hdmi/video clock as mux parent

The meson_vclk code from the display driver may change the rate of the
video clock. Therefore better don't use it as pwm mux parent.
After removing this clock from the parent list pwm_gxbb_data and
pwm_g12a_ee_data are the same as pwm_meson8b_data. So we can remove
them.

Reported-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>