drivers: bbled: pwm: mchp: BBLED low power mode updated

Updated the driver to support low power mode.
Introduced "enable-low-power" flag in device tree to
control(on/off) low power mode.

If flag added in DTS, during sleep BBLED will switch off the LEDs.
Otherwise BBLED will continue the configured blinking pattern on LEDs.

Signed-off-by: Manimaran A <manimaran.a@microchip.com>