configure: show adapter Xilinx XVC/PCIe in the configuration summary

configure: show adapter Xilinx XVC/PCIe in the configuration summary

Adapter Xilinx XVC/PCIe was not appearing in the configuration summary
because of the wrong variable name: build_xlnx_pcie_xvc
instead of enable_xlnx_pcie_xvc.

Also build this adapter automatically on Linux.

Change-Id: I69ea92f550052b9ce55ce32597ac446a15a87388
Signed-off-by: R. Diez <rdiezmail-openocd@yahoo.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8312
Tested-by: jenkins
Reviewed-by: R. Diez <rdiez-2006@rd10.de>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>