drm/i915: add support for perf configuration queries

Listing configurations at the moment is supported only through sysfs.
This might cause issues for applications wanting to list
configurations from a container where sysfs isn't available.

This change adds a way to query the number of configurations and their
content through the i915 query uAPI.

v2: Fix sparse warnings (Lionel)
    Add support to query configuration using uuid (Lionel)

v3: Fix some inconsistency in uapi header (Lionel)
    Fix unlocking when not locked issue (Lionel)
    Add debug messages (Lionel)

v4: Fix missing unlock (Dan)

v5: Drop lock when copying config content to userspace (Chris)

v6: Drop lock when copying config list to userspace (Chris)
    Fix deadlock when calling i915_perf_get_oa_config() under
    perf.metrics_lock (Lionel)
    Add i915_oa_config_get() (Chris)

Link: https://gitlab.freedesktop.org/mesa/mesa/merge_requests/932


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/20191014201404.22468-2-chris@chris-wilson.co.uk