pinctrl: Add PIN_CONFIG_MODE_PWM to enum pin_config_param

pinctrl: Add PIN_CONFIG_MODE_PWM to enum pin_config_param

It seems that we will have more and more pin controllers that support
PWM function on the (selected) pins. Due to it being a part of pin
controller IP the idea is to have some code that will switch the mode
and attach the corresponding driver, for example, via using it as
a library. Meanwhile, put a corresponding item to the pin_config_param
enumerator.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210412140741.39946-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>