gpiolib: Add gpio name information to /sys/kernel/debug/gpio

Add some information about gpio names to the debugfs gpio file. name and
label of a GPIO are then displayed next to each other. This way it is
easy to see what the real name of GPIO is and what the driver requested
it for.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
[Dropped unsolicited sysfs ABI patch hunk]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>