drm/i915: Sanitycheck PCI BARs

For proper operation of i915 we need usable PCI GTTMMADDR BAR 0
(1 for GEN2). In most cases we also need usable PCI GFXMEM BAR 2.
Let's add functions to check if BARs are set, and that it have
a size greater than 0.
In case GTTMMADDR BAR, let's validate at the beginning of i915
initialization.
For other BARs, let's validate before first use.

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220805155959.1983584-3-piotr.piorkowski@intel.com