driver/ddr/fsl: Add general MMDC driver and reuse common MMDC driver for ls1012a

This general MMDC driver adds basic support for Freescale MMDC
(Multi Mode DDR Controller). Currently MMDC is integrated on ARMv8
LS1012A SoC for DDR3L, there will be a update to this driver to
support more flexible configuration if new features (DDR4, multiple
controllers/chip selections, etc) are implimented in future.

Meantime, reuse common MMDC driver for LS1012ARDB/LS1012AQDS/
LS1012AFRDM.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>