boards: nxp: pinmux: enable ftm pwm outputs based on DT_INST_* defines

Enable the NXP FTM PWM outputs in the board pinmux files based on the
DT_INST_* defines instead of CONFIG_PWM_* to match the pwm_mcux_ftm
driver.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>