drm - Move startup delay to VERSION ioctl

drm - Move startup delay to VERSION ioctl

* We had a startup delay in the i915 attach path, which is
  synchronous with the kldload that X does.  Unfortunately, this
  doesn't appear to work well, probably because it just stalls
  everything and leaves the race intact after the sleep returns.
  Also, the kld lock is held across the sleep.

* Move the startup delay to the first call of the DRM_IOCTL_VERSION
  ioctl.  This is outside the kld path allows drm to free-run while
  simply imposing a short delay on the X startup to give the drm
  system time to stabilize.

* Should fix several intel i915 startup issues that can leave the
  screen corrupt, and perhaps other startup issues.