rp2040: hardware PWM support

This implements hardware PWM support for the rp2040. The maximum
value(100% duty) is set to 255 to match the other controllers. Cycle
time is clamped automatically, and uses the full 8.4 fractional range of
the rp2040 PWM block. This allows a maximum PWM frequency of 490kHz and
a minimum frequency of 1915 Hz.

Signed-off-by: Lasse Dalegaard <dalegaard@gmail.com>

src/rp2040/Kconfig

@@ -10,6 +10,7 @@ config RP2040_SELECT
     select HAVE_GPIO_BITBANGING
     select HAVE_STRICT_TIMING
     select HAVE_CHIPID
+    select HAVE_GPIO_HARD_PWM
 
 config BOARD_DIRECTORY
     string