bus/a2bus: Add Uthernet II support Wiznet w5100

[ksherlock]

a2RetroSystems Uthernet II / Wiznet W5100/W5100S emulation

Wiznet W5100

Used in: Uthernet II (Apple II), Spectranet (ZX Spectrum)

Based on:

W5100, W5100S, W5200, W5500 datasheets WIZnet ioLibrary Driver (https://github.com/Wiznet/ioLibrary_Driver) https://docs.wiznet.io/Product/iEthernet/W5100/ Uthernet II User's and Programmer's Manual Testing with Uthernet II and W5100S-EVB-Pico

High-level UDP/TCP/ICMP emulation is included, which attempts to match the quirks.

With the Uthernet II it's often only used as a raw ethernet device (ip65, marinetti, a2osx) but there is some software that uses the TCP stack, eg A2stream

mame apple2ee -sl3 uthernet2  -flop1 A2Stream.dsk

[ksherlock]

I've rewritten it to move all the registers into discrete fields and split the sockets into a separate device to simplify their registers and tcp/udp support. The w5100s support was also removed to keep things simple since it's not needed for the Uthernet II card.