drm/i915: Update DRIVER_DATE to 20170418

#define DRIVER_NAME		"i915"

#define DRIVER_DESC		"Intel Graphics"

#define DRIVER_DATE		"20170403"

#define DRIVER_TIMESTAMP	1491198738

#define DRIVER_DATE		"20170418"

#define DRIVER_TIMESTAMP	1492507096

/* Use I915_STATE_WARN(x) and I915_STATE_WARN_ON() (rather than WARN() and

 * WARN_ON()) for hw state sanity checks to check for unexpected conditions