Change in coreboot[master]: mb/intel/shadowmountain: Add bootblock and verstage code

[V Sowmya (Code Review)]

Attention is currently required from: Nico Huber, Martin Roth, Tim Wawrzynczak, Sugnan Prabhu S, Subrata Banik, Angel Pons, Balaji Manigandan, Aamir Bohra.
V Sowmya has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/49479 )

Change subject: mb/intel/shadowmountain: Add bootblock and verstage code
......................................................................

Patch Set 7:

(3 comments)

Patchset:

PS6:
> Selection of CHROMEOS seems unwarranted and should be explained in detail.

I have removed the selection and will handle it from the config.<board>.

File src/mainboard/intel/shadowmountain/Kconfig:

https://review.coreboot.org/c/coreboot/+/49479/comment/c682f53b_91413718 
PS5, Line 24: default y
> If that is true, this is the first board that requires CHROMEOS […]

I have removed the selection and will handle it from the config.<board> [https://review.coreboot.org/c/coreboot/+/50118]

File src/mainboard/intel/shadowmountain/Kconfig:

https://review.coreboot.org/c/coreboot/+/49479/comment/c575c9a1_5f7a974c 
PS6, Line 6: 	select CHROMEOS
> @Sowmya, you don't need to select this by default.

Done