drm/i915/bxt: Add BXT PCI ids

drm/i915/bxt: Add BXT PCI ids

v2: Switch to info->ring_mask and add VEBOX support.
v3: Fold in update from Damien.
v4: Add GEN_DEFAULT_PIPEOFFSETS and IVB_CURSOR_OFFSETS
v5: set no-LLC (imre)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com> (v1,v4)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v4)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>