arm64: dts: actions: s900-bubblegum-96: Add gpio line names

Add gpio line names to Actions Semi S900 based Bubblegum-96 board.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>