ENGR00225700: ARM: mx6sl: Fix suspend/resume lockup

ENGR00225700: ARM: mx6sl: Fix suspend/resume lockup

Currently, the sequence and functionality we use to enter and exit
suspend causes us to hang upon resuming.  It appears that this is being
caused by two things.  The first is the powering off of the 2p5 rail
which powers the IO pullups and  pulldowns.  The DQS pins were
configured as pull downs.  The second is switching the DQS pins from
differential to CMOS mode (and back).  This second problem only
occurs on a few EVK boards.

It is believed that these changes are causing glitches on the mmdc DQS
pins which is putting garbage in the FIFO (or causing some other FIFO
problem).  This patch adds two mmdc0 FIFO resets after exiting the
suspend.  Two are thought to be needed per previous FIFO reset
experience by Mike Kjar.

Since the MMDC0 FIFO will be cleaned each time, we can now remove
the code that configured the DQS lines as pull downs as we no
longer care if they float.

Signed-off-by: Robert Lee <robert.lee@freescale.com>