drm/i915: Make intel_dp_is_edp() less specific

All the bits in the VBT child device type have some speciifc meaning,
so looking for an exact match isn't always the right thing. On some
VLVs for example the device type for eDP panels is 0x1806.

If we mask out the bits that could concievably change between different
eDP panels, we are left with the set of bits that should still
tell us if the port is eDP or not.

v2: Use the named bits for VBT child device type

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71051


Tested-by: Robert Hooker <robert.hooker@canonical.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>