riscv: dts: nezha-d1: add gpio-line-names

Add descriptive names so users can associate specific lines with their
respective pins on the 40-pin header according to the schematics.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Link: http://dl.linux-sunxi.org/D1/D1_Nezha_development_board_schematic_diagram_20210224.pdf


Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230210025132.36605-2-twoerner@gmail.com


Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>