iommu: msm: Add debug option to only map 4K pages

For debugging and performance measurements it might be useful to
force mappings into the page tables with 4K granularity. To enable
this feature turn on CONFIG_IOMMU_FORCE_4K_MAPPINGS.

Change-Id: Ie2a36e3f4e2f96b2c19b3b8b64e8f8ed1a13e674
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>