drm: meson: Cleanup on drm_display_mode print str

This patch adjust the print string of drm_display_mode object
to remove drm_mode_object dependency in meson files.

Signed-off-by: Shayenne Moura <shayenneluzmoura@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/7017942bbbb3e0e6c1e2bd854ea5a5f461784ac4.1545308167.git.shayenneluzmoura@gmail.com