drm/i915/perf: prune OA configs

In the following commit we'll introduce loadable userspace
configs. This change reworks how configurations are handled in the
perf driver and retains only the test configurations in kernel space.

We now store the test config in dev_priv and resolve the id only once
when opening the perf stream. The OA config is then handled through a
pointer to the structure holding the configuration details.

v2: Rework how test configs are handled (Lionel)

v3: Use u32 to hold number of register (Matthew)

v4: Removed unused dev_priv->perf.oa.current_config variable (Matthew)

v5: Lock device when accessing exclusive_stream (Lionel)

v6: Ensure OACTXCONTROL is always reprogrammed (Lionel)

v7: Switch a couple of index variable from int to u32 (Matthew)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170803165812.2373-3-lionel.g.landwerlin@intel.com