[M] Change in coreboot[master]: mb/siemens/mc_ehl3: Add PTN3460 eDP-to-LVDS bridge

[Martin Roth (Code Review)]

Attention is currently required from: Uwe Poeche, Werner Zeh, Jan Samek.

Martin Roth has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/70692 )

Change subject: mb/siemens/mc_ehl3: Add PTN3460 eDP-to-LVDS bridge
......................................................................

Patch Set 9:

(4 comments)

Patchset:

PS9: 
A few thoughts.  Feel free to say no, or to do changes in a follow-on patch - up to you.

File src/mainboard/siemens/mc_ehl/variants/mc_ehl3/devicetree.cb:

https://review.coreboot.org/c/coreboot/+/70692/comment/e5c0d484_9ced9d33 
PS9, Line 170: # Add dummy I2C device to limit BUS speed to 100 kHz in OS
             : 			chip drivers/i2c/generic
             : 				register "hid" = ""PRP0001""
             : 				register "speed" = "I2C_SPEED_STANDARD"
             : 				device i2c 0x7f on end
             : 			end
Is this still needed with the addition of the new chip?

File src/mainboard/siemens/mc_ehl/variants/mc_ehl3/lcd_panel.c:

https://review.coreboot.org/c/coreboot/+/70692/comment/004bb27f_0f6b0289 
PS9, Line 34: 6
Nit: Can this be turned into a #define?

https://review.coreboot.org/c/coreboot/+/70692/comment/0071dd97_f85a9769 
PS9, Line 39:  @return  -1 on error;
Nit: Any reason not to use enum cb_err?  It seems like it's basically returning success/failure.