docs: migration_guide_4.1: entry for renamed device tree properties

add migration guide after renaming device tree properties
- pin_mask -> pin-mask
- pinmux_mask -> pinmux-mask
- vbatts_pins -> vbatts-pins
- bit_per_gpio -> bit-per-gpio
- off_val -> off-val
- on_val -> on-val

Signed-off-by: Jilay Pandya <jilay.pandya@outlook.com>