drm/i915: enable MCHBAR if needed

Using the new PNP resource checking code, this patch allows the i915
driver to allocate MCHBAR space if needed and use the BAR to determine
current memory settings.

[apw@canonical.com: moved to the new generic PNP resource interface]
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
failure to update-index after git-am --reject to hand-apply

Signed-off-by: Eric Anholt <eric@anholt.net>