imx: mx7ulp: Implement the clock functions for i2c driver

Implement the i2c clock enable and get function for mx7ulp. These
functions are required by imx_lpi2c driver.

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