drm/i915/gt: Mark up intel_rps.active for racy reads

We read the current state of intel_rps.active outside of the lock, so
mark up the racy access.

[  525.037073] BUG: KCSAN: data-race in intel_rps_boost [i915] / intel_rps_park [i915]
[  525.037091]
[  525.037103] write to 0xffff8881f145efa1 of 1 bytes by task 192 on cpu 2:
[  525.037331]  intel_rps_park+0x72/0x230 [i915]
[  525.037552]  __gt_park+0x61/0xa0 [i915]
[  525.037771]  ____intel_wakeref_put_last+0x42/0x90 [i915]
[  525.037991]  __intel_wakeref_put_work+0xd3/0xf0 [i915]
[  525.038008]  process_one_work+0x3b1/0x690
[  525.038022]  worker_thread+0x80/0x670
[  525.038037]  kthread+0x19a/0x1e0
[  525.038051]  ret_from_fork+0x1f/0x30
[  525.038062]
[  525.038074] read to 0xffff8881f145efa1 of 1 bytes by task 733 on cpu 3:
[  525.038304]  intel_rps_boost+0x67/0x1f0 [i915]
[  525.038535]  i915_request_wait+0x562/0x5d0 [i915]
[  525.038764]  i915_gem_object_wait_fence+0x81/0xa0 [i915]
[  525.038994]  i915_gem_object_wait_reservation+0x489/0x520 [i915]
[  525.039224]  i915_gem_wait_ioctl+0x167/0x2b0 [i915]
[  525.039241]  drm_ioctl_kernel+0xe4/0x120
[  525.039255]  drm_ioctl+0x297/0x4c7
[  525.039269]  ksys_ioctl+0x89/0xb0
[  525.039282]  __x64_sys_ioctl+0x42/0x60
[  525.039296]  do_syscall_64+0x6e/0x2c0
[  525.039311]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200309113623.24208-1-chris@chris-wilson.co.uk