extmod/network_wiznet5k: Add Wiznet Ethernet network interface.

Originally based on both stm32/network_wiznet5k and stm32/modnwwiznet5k.

If MICROPY_PY_LWIP is enabled it uses the lwIP TCP stack in MicroPython,
communicating with the Wiznet controller in MACRAW mode.  In this mode it
supports using the INTN pin from Wiznet controller to receive data from an
interrupt trigger.

If lwIP is not enabled, it runs in modnetwork/socket mode providing an
interface to the TCP stack running on the Wiznet controller chip.  In this
mode it includes some updates by @irinakim12 from micropython#8021, most notably
bringing in DHCP support.

Supports defining hardware pins in board config or dynamically set at
runtime.  Sets a default MAC address in the random namespace from board
unique-id.

Signed-off-by: Andrew Leech <[email protected]>