drm/i915: relax uncritical udelay_range() settings

udelay_range(2, 3) is inefficient and as discussions with Jani Nikula
<jani.nikula@linux.intel.com> unnecessary here. This replaces this
tight setting with a relaxed delay of min=20 and max=50. which helps
the hrtimer subsystem optimize timer handling.

Link: http://lkml.org/lkml/2016/12/15/127


Fixes: commit 37ab0810 ("drm/i915/bxt: DSI enable for BXT")
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1481853560-19795-1-git-send-email-hofrat@osadl.org