Atm, we don't disable RPS interrupts and related work items before
resetting the GPU. This may interfere with the following GPU
initialization and cause RPS interrupts to show up in PM_IIR too early
before calling gen6_enable_rps_interrupts() (triggering a WARN there).

Solve this by disabling RPS interrupts and flushing any related work
items before resetting the GPU.

v2:
- split out the common parts of the gt suspend and the new gt reset
  functions (Paulo)
v3:
- remove the check for UMS, it's a NOP nowadays (Daniel)
Reported-by: He, Shuang <shuang.he@intel.com>
Testcase: igt/gem_reset_stats/ban-render
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86644Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>