msm: kgsl: improve active_cnt and ACTIVE state management

Require any code path which intends to touch the hardware
to take a reference on active_cnt with kgsl_active_count_get()
and release it with kgsl_active_count_put() when finished.
These functions now do the wake / sleep steps that were
previously handled by kgsl_check_suspended() and
kgsl_check_idle().

Additionally, kgsl_pre_hwaccess() will no longer turn on
the clocks, it just enforces via BUG_ON that the clocks
are enabled before a register is touched.

Change-Id: I31b0d067e6d600f0228450dbd73f69caa919ce13
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>