cmd: gpio: Skip output on -ENOENT

On the Renesas RZ/G2L SoC family, valid GPIO numbers are not contiguous.
This is determined by the device tree, where a fixed number of bits are
used for the 'pin' number within a 'port', even though not all ports
have the same number of pins. The device tree can't be changed here
without breaking backwards compatibility in Linux, which we don't want
to do.

To avoid printing a status for each of these invalid GPIO numbers when
a user executes `gpio status -a`, we allow gpio_get_function() to return
-ENOENT when the given offset does not refer to a valid GPIO pin and we
skip printing anything if this occurs.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>