drm/i915/selftests: Only query RAPL for integrated power measurements

RAPL provides an on-package power measurements which does not encompass
discrete graphics, so let's avoid using the igfx masurements when testing
dgfx. Later we will abstract the simple librapl interface over hwmon so
that we can verify basic power consumption scenarios.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210412090526.30547-3-matthew.auld@intel.com

drm/i915/selftests: Move gpu energy measurement into its own little lib

Move the handy utility to measure the GPU energy consumption using RAPL
msr into a common lib so that it can be reused easily.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417152018.13079-1-chris@chris-wilson.co.uk