ARM64: dts: meson-gx: use specific compatible for the AO pwms

Use the specific compatible for AO pwms so the pwms input can
be correctly set

FDIV4 is not present on the pwm A0, so change kadhas vim input
clocks to xtal.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>