msm: kgsl: Only check GPU hardware idle while bootstrapping

Use adreno_spin_idle() instead of adreno_idle() to
check status of commands written directly to ringbuffer.
adreno_spin_idle() is preferred because it only checks
the GPU RBBM status whereas adreno_idle() waits for dispatcher
to idle and then waits for GPU hardware to idle.
When writing commands directly to ringbuffer, the status of
dispatcher is immaterial to check.

CRs-fixed: 689304
Change-Id: I43397cd7d5075d061acf6320102548451b57928a
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>