Change in coreboot[master]: mb/intel/shadowmountain: Add the romstage code

[V Sowmya (Code Review)]

Attention is currently required from: Martin Roth, Tim Wawrzynczak, Angel Pons, Balaji Manigandan, Aamir Bohra.
V Sowmya has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/49731 )

Change subject: mb/intel/shadowmountain: Add the romstage code
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Patch Set 5:

(2 comments)

File src/mainboard/intel/shadowmountain/variants/baseboard/memory.c:

https://review.coreboot.org/c/coreboot/+/49731/comment/b17ce636_698fac45 
PS4, Line 8: 	/* DQ CPU<>DRAM map */
> nit: this comment refers to `. […]

Done

https://review.coreboot.org/c/coreboot/+/49731/comment/bda73fa6_d90b3454 
PS4, Line 74: 	gpio_t spd_gpios[] = {
> could this array be const?

Done