msm: kgsl: Get rid of a6xx_hfi_send_req function

Instead, directly call a6xx_hfi_send_generic_req. Also,
get rid of a6xx_hfi_send_get_value() as it is not used.

Change-Id: Idee3af33ff0e5e03a9f974c535f8bc1c7579d492
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>