gpio: mxs: add name_to_gpio() function

gpio: mxs: add name_to_gpio() function

Override the default name_to_gpio() function with one that
accepts strings of the form bank:pin.  If a colon is present
in the provided name, it behaves like the default version.

This lets the "gpio" command work with sane names rather than
requiring the user to enter the bank/pin composite in decimal.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>