ENGR00221970 MX6SL:Fix suspend/resume issue on MX6SLEVK

ENGR00221970 MX6SL:Fix suspend/resume issue on MX6SLEVK

Make sure the Pull Ups are enabled on the DQS lines of
LPDDR2 memory. Without that its possible that the data
latched by the memory will be incorrect when exiting from
self-refresh mode. So only set the drive strengths to 0
when floating the DDR IO pads before entering suspend.

Also never float the CKE pad, this pin always needs to be
driven, else the DDR may incorrectly exit self-refresh.
Hence remove the line that was setting CKE drive strength
to zero (GRP_CTLDS).

Signed-off-by: Ranjani Vaidyanathan <ra5478@freescale.com>