ENGR00255481 mx6: Update equation for thermal sensor

Use universal equation and 25C's calibration data to
get thermal sensor's ratio.

Signed-off-by: Anson Huang <b20788@freescale.com>
ENGR00256543 mx6: Update equation for thermal sensor on i.MX6DL

Use universal equation and 25C's calibration data to
get thermal sensor's ratio on i.MX6DL.

Signed-off-by: Anson Huang <b20788@freescale.com>