pwm: meson: Support constant and polarity bits

pwm: meson: Support constant and polarity bits

Newer meson PWM IPs support constant and polarity bits. Support them to
correctly implement constant and inverted output levels.

Using constant bit allows to have truly stable low or high output level.
Since hi and low regs internally increment its values by 1 just writing
zero to any of them gives 1 clock count impulse. If constant bit is set
zero value in hi and low regs is not incremented.

Using polarity bit instead of swapping hi and low reg values allows to
correctly identify inversion in .get_state().

Signed-off-by: George Stark <gnstark@salutedevices.com>
Link: https://lore.kernel.org/r/20241119125318.3492261-3-gnstark@salutedevices.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>