Revert "[ARM] msm: iommu_domains: replace vmalloc with kmalloc"

When overmapping is used, system can request higher order page allocaitons.
this can lead to page allocation failure if kmalloc is used

CRs-Fixed: 571753

This reverts commit 191a48ee.

Change-Id: I4d44bf88d84d96d315f89a1304a2d25b75be79d8
Signed-off-by: Srinivasarao P <spathi@codeaurora.org>