This adds the basic functionality to emulate a Tulip NIC.

Implemented are:

- RX and TX functionality
- Perfect Frame Filtering
- Big/Little Endian descriptor support
- 93C46 EEPROM support
- LXT970 PHY

Not implemented, mostly because i had no OS using these functions:

- Imperfect frame filtering
- General Purpose Timer
- Transmit automatic polling
- Boot ROM support
- SIA interface
- Big/Little Endian data buffer conversion

Successfully tested with the following Operating Systems:

- MSDOS with Microsoft Network Client 3.0 and DEC ODI drivers
- HPPA Linux
- Windows XP
- HP-UX

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Message-Id: <20191022155413.4619-1-svens@stackframe.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>