riscv: dts: thead: Add Lichee Pi 4M GPIO line names

Add names for the GPIO00-GPIO14 lines of the SO-DIMM module.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Thomas Bonnefille <thomas.bonnefille@bootlin.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Drew Fustini <dfustini@tenstorrent.com>