This driver implements the HW WATCHDOG functions. Which needs
to set CONFIG_HW_WATCHDOG to use them. This is disabled by default for
mx7ulp.

Use watchdog for reset cpu. Implement this in the driver.
Need to define CONFIG_ULP_WATCHDOG to build it.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>