gpio: mxs: Remove unused .id_table support

mxs is a devicetree-only platform and hence it does not make use
of the id_table mechanism.

Get rid of the .id_table as it is unused.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20201118191938.32693-1-festevam@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>