Revert "update rpi-display-overlay.dts pins for 5.10+"

This reverts commit 97d1b136.

The fbtft backlight problem was fixed in 5.15.6 so this workaround has to
be reverted to make backlight work again.

Ref: https://github.com/notro/fbtft/issues/571



Signed-off-by: Noralf Trønnes <noralf@tronnes.org>