ARM: dts: am335x-boneblack.dts: unique gpio-line-names

ARM: dts: am335x-boneblack.dts: unique gpio-line-names

Based on linux-gpio discussion [1], it is best practice to make the
gpio-line-names unique. Generic names like "[ethernet]" are replaced
with the name of the unique signal on the AM3358 SoC ball corresponding
to the gpio line. "[NC]" is also renamed to the standard "NC" name to
represent "not connected".

[1] https://lore.kernel.org/linux-gpio/20201216195357.GA2583366@x1/

Signed-off-by: Drew Fustini <drew@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>