pds_core: Clear BARs on reset

During reset the BARs might be accessed when they are
unmapped. This can cause unexpected issues, so fix it by
clearing the cached BAR values so they are not accessed
until they are re-mapped.

Also, make sure any places that can access the BARs
when they are NULL are prevented.

Fixes: 49ce92fb

 ("pds_core: add FW update feature to devlink")
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/20240129234035.69802-6-brett.creeley@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>