drm/i915: Use ktime on wait_for

We use jiffies to determine when wait expires. However
Imre did find out that jiffies can and will do a >1
increments on certain situations [1]. When this happens
in a wait_for loop, we return timeout errorneously
much earlier than what the real wallclock would say.

We can't afford our waits to timeout prematurely.
Discard jiffies and change to ktime to detect timeouts.

v2: added bugzilla entry (Imre), added stable (Chris)

Reported-by: Imre Deak <[email protected]>
References: https://lkml.org/lkml/2018/4/18/798 [1]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105771
Cc: Imre Deak <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Cc: <[email protected]>
Signed-off-by: Mika Kuoppala <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

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