drm/i915/perf: add more debug message on perf open & configs

This will make it easier to spot issues related to config
creation/usage.

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/20180326090831.22686-9-lionel.g.landwerlin@intel.com