CHERRY-PICK: drm/i915: Retry reading the PCH FDI receiver ISR

CHERRY-PICK: drm/i915: Retry reading the PCH FDI receiver ISR

According to the PRM (Vol3P2), the PCH FDI receiver ISR read for bit lock
should be retried at least once. This patch retries the read 5 times
with a small delay in between reads. I've had reports of display corruption
on resume with "FDI train 1 fail!", so I'm hoping that adding this retry
will mitigate the issue.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
(cherry picked from commit fa37d39e4c6622d80bd8061d600701bcea1d6870)

BUG=chrome-os-partner:7439
TEST=Tested on lumpy with auto suspend/resume script

Change-Id: I8eb18050ddaadd91c5a2a06f4b664f5a3ea65c7f
Reviewed-on: https://gerrit.chromium.org/gerrit/17238
Tested-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Commit-Ready: Sean Paul <seanpaul@chromium.org>