ARM64: defconfig: enable the leds-pwm driver and default-on trigger

This enables the leds-pwm driver to support LEDs which are PWM-powered
(and thus dimmable). Additionally we have to enable the "default-on"
trigger - this was not required before because the gpio-leds driver has
a separate "default-state" property which can be used to enable the LED
by default.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>