[fpv,pinmux] Can we keep a single fpv pinmux_tb

### Description

The fpv flow for pinmux has two testbench tops

- hw/ip/pinmux/fpv/tb/pinmux_tb.sv
- hw/top_earlgrey/ip_autogen/pinmux/tpv/tb/pinmux_tb.sv

They differ in various mio and dio attributes, mostly pad_type and scan_role. The one under top_earlgrey assigns these attributes per pin, while the one under hw/ip makes a blanket assignment to all mio and dios.

I will preserve this dichotomy when transitioning pinmux to ipgen, placing both tb's each with a separate core file under ip_templates, so ip_autogen will keep them. However, I wonder why we need to have both at all. There are a few contributors to these files, most significantly @cindychip and @msfschaffner, and their feedback would be valuable. However, both have transitioned to other principal projects.