drm/i915: Check for fused or unused pipes

drm/i915: Check for fused or unused pipes

We may have fused or unused pipes in our system. Let's check that the pipe
in question is within limits of accessible pipes. In case, that we are not
able to access the pipe, we return early with a warning.

v2: Rephrasing of the commit message (Jani)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103206
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jaswinder Singh Rajput <jaswinder@perfectintelligent.com>
Suggested-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1513584243-12607-1-git-send-email-mika.kahola@intel.com
(cherry picked from commit 0b7029b7e43fda1304c181a3ade0b429b9edcd9d)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v4.10+