drm/i915: reinit status page registers after gpu reset

This fixes gpu reset on my gm45 - without this patch the bsd thing is
forever stuck since the seqno updates never reach the status page.

Tbh I have no idea how this ever worked without rewriting the hws
registers after a gpu reset.

To satisfy my OCD also give the functions a bit more consistent names:
- Use status_page everywhere, also for the physical addressed one.
- Use init for the allocation part and setup for the register setup
  part consistently.

Long term I'd really like to share the hw init parts completely
between gpu reset, resume and driver load, i.e. to call
i915_gem_init_hw instead of the individual pieces we might need.

v2: Add the missing paragraph to the commit message about what bug
exactly this patch here fixes.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65495


Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: lu hua <huax.lu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>