soc: fsl: Correct MAINTAINERS database (SOC)

MAINTAINERS lacks of proper coverage for FSL headers. Fix it accordingly.

Fixes: 1b48706f ("MAINTAINERS: add entry for Freescale SoC drivers")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>