mmc: fsl_esdhc: make GPIO support optional

There would be compiling error as below when enable driver model for esdhc.
undefined reference to `dm_gpio_get_value'
undefined reference to `gpio_request_by_name_nodev'
This patch is to make GPIO support optional with CONFIG_DM_GPIO. Because
all boards of QorIQ platform don't need it and they just check register for
CD/WP status, only some boards of i.MX platform require this.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: York Sun <york.sun@nxp.com>