drm/i915: fix hdmi portclock limits

In

commit 325b9d04
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Apr 19 11:24:33 2013 +0200

    drm/i915: fixup 12bpc hdmi dotclock handling

I've errornously claimed that we don't yet support the hdmi 1.4
dotclocks > 225 MHz on Haswell. But a bug report and a closer look at
the wrpll table showed that we've supported port clocks up to 300MHz.

With the new code to dynamically compute wrpll limits we should have
no issues going up to the full 340 MHz range of hdmi 1.4, so let's
just use that to fix this regression. That'll allow 4k over hdmi for
free!

v2: Drop the random hunk that somehow slipped in.

v3: Cantiga has the original HDMI dotclock limit of 165MHz. And also
patch up the mode filtering. To do so extract the dotclock limits into
a little helper function.

v4: Use 300MHz (from Bspec) instead of 340MHz (upper limit for hdmi
1.3), apparently hw is not required to be able to drive the highest
dotclocks. Suggested by Damien.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67048
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67030


Tested-by: Andreas Reis <andreas.reis@gmail.com> (v2)
Cc: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>