drm/i915/gvt: ensure gpu is powered before do i915_gem_gtt_insert

drm/i915/gvt: ensure gpu is powered before do i915_gem_gtt_insert

i915_gem_gtt_insert may evict some vmas and access HW if ggtt
vm space is not enough. So add mmio_hw_access_pre before invoke
i915_gem_gtt_insert to avoid call trace like below in vgpu create/
destroy test.

WARNING: CPU: 6 PID: 8720 at drivers/gpu/drm/i915/intel_drv.h:1768
assert_rpm_wakelock_held.part.2+0x27/0x30 [i915]
RPM wakelock ref not held during HW access

Call Trace:
  [<ffffffff99af3b22>] dump_stack+0x19/0x1b
  [<ffffffff9948e338>] __warn+0xd8/0x100
  [<ffffffff9948e3bf>] warn_slowpath_fmt+0x5f/0x80
  [<ffffffffc0d5cc32>] assert_rpm_wakelock_held.part.2+0x27/0x30 [i915]
  [<ffffffffc0c7ffcf>] intel_runtime_pm_get_noresume+0x6f/0x80 [i915]
  [<ffffffffc0ca614d>] i915_gem_request_alloc+0x2dd/0x3c0 [i915]
  [<ffffffffc0c9056e>] i915_gem_switch_to_kernel_context+0xae/0x1d0 [i915]
  [<ffffffffc0c91572>] ggtt_flush+0x12/0x30 [i915]
  [<ffffffffc0c917ef>] i915_gem_evict_something+0x25f/0x470 [i915]
  [<ffffffffc0c9b62c>] i915_gem_gtt_insert+0x15c/0x1c0 [i915]
  [<ffffffffc0d35837>] alloc_gm+0xa7/0x160 [i915]
  [<ffffffffc0d35d8d>] intel_vgpu_alloc_resource+0x1ad/0x410 [i915]
  [<ffffffffc0d4819c>] intel_gvt_create_vgpu+0x16c/0x260 [i915]
  [<ffffffffc055d980>] intel_vgpu_create+0x50/0x140 [kvmgt]
  [<ffffffffc04fc6fa>] mdev_device_create+0x1aa/0x2e0 [mdev]

v2: use mmio_hw_access_pre/post <Zhenyu>

Signed-off-by: Hang Yuan <hang.yuan@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>