drivers: pwm: Add PWM capture functionality for pwm_mcux

Add support for PWM input capture functionality to the NXP MCUX PWM
driver. This enables measurement of pulse width and period of external
PWM signals.

Key features added:
- PWM capture configuration and control APIs
- Interrupt-driven capture with overflow handling
- Support for both pulse width and period measurement
- Configurable input filtering
- Support for continuous and one-shot capture modes

The implementation uses FlexPWM channel X as the dedicated input
capture channel, while channels 0 and 1 remain available for PWM
output. Capture functionality is conditionally compiled based on
CONFIG_PWM_CAPTURE configuration option.

Signed-off-by: Felix Wang <fei.wang_3@nxp.com>