[RSDK-12176] warn when pwm config is missing

[npmenard]

Give user context if hardware pwm pins cannot be used
see viam-modules/pinctrl#27

[JohnN193]

haven't used this part of the board config before, but would we be able to support the setting through the board_settings attribute as well?

[npmenard]

haven't used this part of the board config before, but would we be able to support the setting through the board_settings attribute as well?

IMO it is bad design to change a config file in the boot process without any regards to potential configuration conflicts
The default behavior is to use software PWM which should be enough for most cases so I don't think we need the change the config for the user