ARM: imx: ensure dsm_request signal is not asserted when setting LPM

There is a defect in imx6 LPM design.  When SW tries to enter low power
mode with following sequence, the chip will enter low power mode before
A9 CPU execute WFI instruction:

1. Set CCM_CLPCR[1:0] to 2'b00;
2. ARM CPU enters WFI;
3. ARM CPU wakeup from an interrupt event, which is masked by GPC or not
   visible to GPC, such as interrupt from local timer;
4. Set CCM_CLPCR[1:0] to 2'b01 or 2'b10;
5. ARM CPU execute WFI.

Before the last step, the chip will enter WAIT mode if CCM_CLPCR[1:0] is
set to 2'b01, or enter STOP mode if CCM_CLPCR[1:0] is set to 2'b10.

The patch implements a recommended workaround for this issue.

1. SW triggers irq #32(IOMUX) to be always pending manually by setting
   IOMUX_GPR1_GINT bit;
2. SW should then unmask it in GPC before setting CCM LPM;
3. SW should mask it right after CCM LPM is set (bit0-1 of CCM_CLPCR).

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

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