msm: kgsl: Bypass GMU write/read buffers

Write/read buffers in GMU are not ready to use in SDM845. Disable
them to avoid potential stability issue.

CRs-Fixed: 2085877
Change-Id: I2f64323a5f75027ae2987cee51bcf42dd7597d1d
Signed-off-by: George Shen <sqiao@codeaurora.org>