drm: i915: Cleanup drm_display_mode print str

This patch adjust the print string of drm_display_mode object
to remove drm_mode_object dependency in i915 files.
It modifies the print style to standardize the use of DRM_MODE_FMT.

Signed-off-by: Shayenne Moura <shayenneluzmoura@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/087e07a388c7c65b6d0ec50db069640e4eb32fdf.1545308167.git.shayenneluzmoura@gmail.com