pinctrl: meson: meson8: add the PWM pins

This adds the missing pins for the PWM controllers found in Amlogic
Meson8 SoCs. This includes the pins for PWM_A, PWM_B, PWM_C, PWM_D,
PWM_E and PWM_F controllers.
There is an additional PWM function with the name PWM_VS in the vendor
kernel sources which seems to be used for external video input. Thus
it's not part of this change as the IP block behind the pwm-meson driver
is not responsible for these pins.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>