BREAKING CHANGE: remove PWM_MULTICHAN option
PWM_MULTICHAN option is redundant, we can just set CONFIG_PWM_NCHANNELS > 1.
At default CONFIG_PWM_NCHANNELS is set to 1, so the default behavior is preserved.
Access to single channel API is now `info->channels[0].XXX` instead of `info->XXX`
This is the first step to simplify PWM implementation and make it more portable.
Signed-off-by: raiden00pl <raiden00@railab.me>