drivers: eth_smsc911x: Add driver for SMSC9118 aka LAN9118 chip

As emulated by QEMU. SMSC9118 is compatible with SMSC9220 as used in
ARM MPS2 board, as well as SMSC9115/6/7/etc. devices.

Portions of the code are based on mbedOS code from its
targets/TARGET_ARM_SSG/TARGET_CM3DS_MPS2/device/drivers/smsc9220_eth.c

eth_smsc9220_priv.h originally comes from Arm mbedOS file:

targets/TARGET_ARM_SSG/TARGET_CM3DS_MPS2/device/drivers/smsc9220_eth.h

augmented with struct & defines from:

targets/TARGET_ARM_SSG/TARGET_CM3DS_MPS2/device/CM3DS.h

and renamed as eth_smsc911x_priv.h to follow Zephyr conventions.

Then, following changes applied:

Changes to build under Zephyr, changes to use symbolic constants
and field access helpers, typo fixes, etc.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>