uftdi.4: Makeover!

+ tag SPDX
+ rewrite document description to one line in contemporary style
+ rewrite synopsis in vt/iwx/mtw/uart's style, adding all sysctls

for brevity, in the future I will call this "possibilities style"

+ move ioctls into an ioctl section (we should use these more)
+ add a sysctl section listing all sysctls and their defaults
+ remove list of specific 20 year old usb serial adapters from hardware
+ move list of supported controllers to the hardware section
+ explain how the driver is loaded in description, and give usage hints

MFC after: 3 days
Thanks: cperciva (devd calls devmatch at runtime)
Thanks: linimon (you dont need to be able to read *)
Thanks: adrian (here, you can find things in the code)
Reviewed by: adrian, ivy, mhorne (previous version)
Differential Revision: https://reviews.freebsd.org/D50608