ENGR00209501 [MX6]Support different platforms DDR IO setting in DSM

ENGR00209501 [MX6]Support different platforms DDR IO setting in DSM

As Mx6 dq, dl and sl have different DDR IO address, so
we need to do the DDR IO low power setting according
to different CPU type.

Also, Mx6sl has some different config in DSM, need to
separate it from other platforms.

Change mx6q_suspend to mx6_suspend, as it is a common
thing for all mx6 platforms.

Add rtc driver for mxsl platform to support suspend/resume test.

Signed-off-by: Anson Huang <b20788@freescale.com>