ARM: imx: add anatop settings for LPDDR2 when enter DSM mode

For LPDDR2 platform, no need to enable weak2P5 in DSM mode,
it can be pulled down to save power(~0.65mW).

And per design team's recommendation, we should disconnect
VDDHIGH and SNVS in DSM mode on i.MX6SL.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>