drm/i915: Print error state times relative to capture

Using plain jiffies in error state output makes the output
time differences relative to the current system time. This
is wrong as it makes output time differences dependent
of when the error state is printed rather than when it is
captured.

Store capture jiffies into error state and use it
when outputting the state to fix time differences output.

v2: use engine timestamp as epoch, output formatting (Chris)
v3: pass epoch to print_engine/request (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430075259.4476-1-mika.kuoppala@linux.intel.com