msm: kgsl: Calculate the offset of context bank 0

The context bank 0 offset and size of each context bank register space
was hardcoded. The context bank 0 offset changed in A660. We now compute
these values from GPU_GFX_SMMU_IDR1 register instead of using hardcoded
values.

Change-Id: If9125dfe823f92e9c61ff1635ae07a13ec6f000b
Signed-off-by: Raghu Ananya Arabolu <rarabolu@codeaurora.org>