dim: allow all developer commands without full setup

Requested by Arek (so CI can use sparse/checkpatch) and Chris (because
it's more useful for developers this way).

v2: Remove debug leftover. Oops (Chris).

v3: dim retip requires the integration configuration to figure out
where drm-tip is:
- Read the integration config even for developer cmds, but only when
  available.
- Add a fallback trick for dim retip to make a good educated guess
  about where drm-tip is.

v4: Add break (Chris, Gustavo)

Acked-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>