drivers: pwm: rpi_pico: Configuring the divide ratio adaptively

If the `divider-int-0` or variations of these for each channel properties
are not specified, or if these is 0,
the driver dynamically configures the division ratio by specified cycles.

The driver will operate at the specified division ratio if a non-zero
value is specified for `divider-int-0`.
This is unchanged from previous behavior.

Please specify ``divider-int-0`` explicitly to make the same behavior as
before.

In addition, the default device tree properties related to the division
ratio have been removed.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>