usb: dwc3: msm: Attach IOMMU before DMA allocations

During dwc3_msm_probe() when of_platform_populate() is called, the
the dwc3 child probes and calls dwc3_gadget_init() which will
make several calls to allocate DMA memory. If IOMMU is used, make
sure that it is attached prior to this. We can detach it afterwards
and it will be reattached on subsequent connection/resume when
dwc3_msm_resume() is called. Also during resume, call attach before
performing dwc3_msm_power_collapse_por() which is performing DMA
allocations for re-init.

Change-Id: I38ee511c7f2cef1d6d01a4479c2c4f498efc048c
Signed-off-by: Jack Pham <jackp@codeaurora.org>