drm/i915: Simplify PSR debugfs

for igt test case.

v2: remove trailing spaces and fix conflicts

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
[danvet:
- make it comipile
- s/IS_HASWELL/HAS_PSR/]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>