Add techmap for BUFGMUX

[rw1nkler]

This commit adds techmap for BUFGMUX.
The implementation is based on the [Xilinx documentation]

[litghost]

Please add a test for this techmap:

• Add a test circuit
• Test it in hardware
• Have a add_vivado_target and make sure the diff test is green

[rw1nkler]

For the Nexys Video board test produces the same error as for OpenTitan design #1442 (comment). I will investigate why this error occurs.

[litghost]

LGTM, merge if green and if tested in hardware

[litghost]

CI is red

[rw1nkler]

Yeah, I thought that we have already merged new db - #1619
Can we merge that? @litghost

[litghost]

Can you simply incorporate the submodule bump in this PR, and that will test that the new prjxray-db solves your issue?

[rw1nkler]

@litghost I believe that those CI failures are not related to this PR.

• Xilinx Series 7 - Vendor Tools Tests fails due to no space left on the device error

Traceback (most recent call last):
  File "/tmpfs/src/github/symbiflow-arch-defs-presubmit-xc7-vendor/xc/common/utils/prjxray_import_tile_capacity.py", line 90, in <module>
    main()
  File "/tmpfs/src/github/symbiflow-arch-defs-presubmit-xc7-vendor/xc/common/utils/prjxray_import_tile_capacity.py", line 86, in main
    f.write(tile_str)
OSError: [Errno 28] No space left on device

• VtR + SymbiFlow Architecture Definitions fails on no possible path error in the buttons_basys3_full test:

Cannot route from BLK-TL-RIOPAD_M[0].IOI_ILOGIC0_O[0] (RR node: 1484735 type: SOURCE location: (114,109) class: 53 capacity: 1 fan-in: 0 fan-out: 1) to BLK-TL-RIOPAD_S[0].IOI_OLOGIC1_D1[0] (RR node: 1392164 type: SINK location: (114,67) class: 26 capacity: 1 fan-in: 1 fan-out: 0) -- no possible path
Failed to route connection from 'sw[15]' to '$iopadmap$top.led_15.t_inv' for net '$abc$1667$iopadmap$led[15]' (#16)

Could this be related to #1711?