msm: kgsl: Change readl to readll for reading 64bit registers

The macro KGSL_IOMMU_GET_CTX_REG_LL  was incorrectly using
readl_relaxed() instead of the correct readll_relaxed().

Change-Id: Ie811161a31257eb58b82d38503c3790528eb8333
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>