drm/i915/gvt: Deliver guest cursor hotspot info

Guest OS driver uses PV info registers to deliver cursor hotspot info
to host. This patch is used to get cursor hotspot info from virtual
registers and deliver it to host userspace.

v4->v5:
- remove CI warning.

v3->v4:
- return UINT_MAX when x_hot/y_hot is invalid. (Zhenyu)
- correct version.

v2->v3:
- add validate_hotspot(). (Zhenyu)

v1->v2:
- name as cursor_x_hot/cursor_y_hot. (Zhenyu)
- use i915_reg_t definition instead of magic numbers. (Zhenyu)

Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>