boards: arm: sam_v71_xult: Enable pwm on led-0

The atmel pwm driver doesn't have a easy way to test and show
functionality to users.  This re-assign led-0 function from
gpio-leds to pwm-leds.  The current led-0 entry at gpio-leds
was keep with status disabled, as refence.  It allows test pwm
driver for SAM Cortex-M7 MCUs.  The led-1 assume Zephyr sample
default led0 alias.

Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>