pwm: meson: Convert to waveform API

The PWM subsystem introduced a new waveform abstraction that
describes a PWM signal by period length, duty length and duty offset
instead of period, duty cycle and polarity. The meson driver still
uses the legacy .apply() and .get_state() callbacks and does not
implement the waveform callbacks, so consumers cannot use the
pwm_*_waveform() helper functions with it.

Adopt the new API by implementing .round_waveform_tohw(),
.round_waveform_fromhw(), .read_waveform() and .write_waveform()
with a private meson_pwm_waveform struct holding the hardware
representation. The cached channel state fields (rate, hi, lo,
constant, inverted) are removed; counter values are now computed in
.round_waveform_tohw() via clk_round_rate() without register writes,
then committed in .write_waveform().

The hardware invert bit places the duty active phase at the end of the
period on revisions that have it. Input clock rates are kept at or
below 1 GHz so each counter cycle remains representable in nanoseconds
by .round_waveform_fromhw(). Requests for which clk_round_rate() cannot
provide such a rate are rejected. Otherwise, period counts above the
16-bit range are clamped, while a zero count is rounded up to one and
signalled by .round_waveform_tohw() returning 1.

Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://patch.msgid.link/20260717-pwm_meson_convert_to_waveform_api-v1-1-d7dbdae1318d@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

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