mx6sabreauto: Do not enable WEIM by default

WEIM cannot be used when I2C3 is enabled due to pin conflict, so keep
WEIM disabled by default.

I2C3 controls GPIO I2C expander (USB host and OTG have VBUS controlled by
the GPIO I2C expander), magnetometer, accelerometer.

Not disabling WEIM in U-Boot causes I2C3 to behave badly when booting
a NXP 4.1 kernel, which leads to probe failure on several devices,
including the lack of USB:

imx_usb 2184000.usb: Can't register ci_hdrc platform device, err=-517

By keeping WEIM disabled in U-Boot these kernel issues are gone.

Reported-by: Takashi Matsuzawa <tmatsuzawa@xevo.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>