msm: npu: Increase IOMMU mapping size to 4GB

The original IOMMU mapping space starts from 0x80000000 with
size 0x60000000 bytes. But actually there is no such limitation
for NPU IOMMU which can start from 0 with size 4GB.

Change-Id: Ic988ca1ae242438d0c5eaede2a3eaab55f8e508e
Signed-off-by: Jilai Wang <jilaiw@codeaurora.org>