msm: kgsl: Use context bank 1 for IOMMU-v2

As of commit 27cfed19 IOMMU-v2 uses context bank 1 for gfx3d_user instead
of context bank 0. Update the context offsets accordingly to access the
registers of the appropriate context bank.

Change-Id: I6c9c2b74e7ea82ec07fb916968bba85e8eb79b3e
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>