icnss2: Add API to perform SMMU unmap

During IPA pipe setup, physical address is  mapped
to IOVA using SMMU API. At the time of IPA cleanup SMMU
unmap API is not called.
Add and export ICNSS API to unmap SMMU mapped memory.
This API should be called during IPA cleanup from host
driver.

Change-Id: If7ad8eee69699adb4cbe6dba8025cb41628b4bb3
Signed-off-by: Mohammed Siddiq <msiddiq@codeaurora.org>