drm/log: Color the timestamp, to improve readability

Color the timesamp prefix, similar to dmesg.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20241204160014.1171469-5-jfalempe@redhat.com