gpio_led: add support for inverted polarity

Some GPIO connected LEDs have inverted polarity.
Introduce new config option: CONFIG_GPIO_LED_INVERTED_TABLE for the
specifying the inverted GPIO LEDs list and add support for this in the
gpio_led driver.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Tested-by: Ilya Ledvich <ilya@compulab.co.il>