usb: gadget: Mark usb gsi driver dma memory as cached

With this change usb gsi driver specific context bank is marked as
cached. This is needed to be in sync with IPA context bank used to
map usb iova to PA which is marked as non-cached. Otherwise IPA is
accessing the cached memory of USB transfer ring which resulting
in to SMMU page fault as the contents of the memory is invalid.
IO-Coherency is enabled by default in driver.

Change-Id: I04790e155f8e82425d98a3bc1a9d558fccd88bcb
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>