res_generic_po device extraction changed from R devices to X devices

[d-m-bailey]

In commit 13a8c5d2b10f1ec959d24bb1c9b580f0abbebe91 the res_generic_po device extraction was changed from R devices to X devices. I think this change enables the extraction of l and w parameters which may have been previously ignored

The corresponding standard cell spice libraries and possible xschem primitive should be modified to correspond.

[RTimothyEdwards]

FYI, the L and W parameters were not previously ignored, as the "R" component in SPICE does have a variation which is a "semiconductor resistor" and takes parameters L and W instead of a resistance value. So the only change needed to the standard cell libraries was to change "R" to "XR". This has been done.