[M] Change in coreboot[master]: soc/intel/ehl: Add EHL MDIO operation

[Mario Scheithauer (Code Review)]

Attention is currently required from: Angel Pons, Lean Sheng Tan, Werner Zeh.

Mario Scheithauer has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/69383 )

Change subject: soc/intel/ehl: Add EHL MDIO operation
......................................................................

Patch Set 4:

(2 comments)

File src/soc/intel/elkhartlake/mdio.c:

https://review.coreboot.org/c/coreboot/+/69383/comment/0952dda1_ce92adfe 
PS3, Line 3: #define __SIMPLE_DEVICE__
> Do we need this even if this file is compiled just for the ramstage?

Ack

File src/soc/intel/elkhartlake/tsn_gbe.c:

https://review.coreboot.org/c/coreboot/+/69383/comment/d867f22e_5b50b865 
PS3, Line 41: %s Cannot find MDIO bus operations
> What about 'MDIO bus operations not available for %s. […]

Done