gpio: Use case-insentive matching on the GPIO name

gpio: Use case-insentive matching on the GPIO name

Allow the 'gpio' command to match GPIO bank names regardless of the case
of each. While these are generally in upper case, it is useful to be able
to provide lower case with the command.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>