drm/i915/perf: introduce a versioning of the i915-perf uapi

Reporting this version will help application figure out what level of
the support the running kernel provides.

v2: Add i915_perf_ioctl_version() (Chris)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191014201404.22468-1-chris@chris-wilson.co.uk