ENGR00233929: add kernel command line to enable snvs

ENGR00233929: add kernel command line to enable snvs

In MX6Q/DL, originally GPIO_0 is used as CKO pin function. when SNVS
module is enabled, CKO output stops suddenly.
Both CKO clock config register CCOSR and GPIO_0 IOMUX register value are
not changed. But because ALT7 of GPIO_0 pad is SNVS_VIO_5 function. I
doubt that when SNVS module is enabled, GPIO_0 pad is automatically
changed to SNVS instance by SoC.
Thus we add option for snvs enable/disable.

Signed-off-by: Terry Lv <r65388@freescale.com>