arm64: dts: qcom: sbc: Name GPIO lines

This names the GPIO lines on the APQ8016 "SBC" also known
as the DragonBoard 410c, according to the schematic. This
is necessary for a conforming userspace looking across
all GPIO chips for the GPIO lines named "GPIO-A" thru
"GPIO-L".

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>