drm/i915: remove single-use GEM_DEBUG_EXEC()

Reduce the magic of what's going on in GEM_DEBUG_EXEC() by expanding it
inline and being explicit about it. It's as single use case anyway, so
the macro feels overkill.

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504183716.987793-2-jani.nikula@intel.com