MAINTAINERS: Update MMC/POWER/FREESCALE QORIQ

- Update MMC entry to match 'mmc' using 'N'
- Add myself as POWER maintainer for regulator and pmic patches. I have
  started to handle relevant patches.
- Update QORIQ maintainer. Priyanka has moved to work on other stuff, I
  have been handling this for quite some time.

Signed-off-by: Peng Fan <peng.fan@nxp.com>