drivers: led: Microchip XEC LED driver using BBLED controller

Implement a LED driver for Microchip XEC using the breathing,
blinking LED controller. The driver supports LED on, off, and
blink API's. The BBLED block uses the 32768 Hz clock domain
allowing the module to operate in light and deep sleep states.
Blink frequency is 32768 divided by 256 * (prescale + 1) where
prescale is a 12-bit value. Duty cycle is specified by an 8-bit
value where 0 = full off, 127 is 50%, and 255 is full on.

Signed-off-by: Jay Vasanth <jay.vasanth@microchip.com>