[XS] Change in coreboot[main]: src/intel/cmm/block: Update sa_get_tseg_size function

[Subrata Banik (Code Review)]

Attention is currently required from: Anil Kumar K, Bora Guvendik, Jamie Ryu, Jeremy Compostella, Wonkyu Kim.

Subrata Banik has posted comments on this change by Wonkyu Kim. ( https://review.coreboot.org/c/coreboot/+/84210?usp=email )

Change subject: src/intel/cmm/block: Update sa_get_tseg_size function
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Patch Set 2:

(1 comment)

File src/soc/intel/common/block/systemagent/systemagent_early.c:

https://review.coreboot.org/c/coreboot/+/84210/comment/332cab5b_3717ae88?usp... :
PS2, Line 155: 	return sa_get_gsm_base() - sa_get_tseg_base();
WDYT? I assume in absence of IGD the GSM size would be zero hence, we won't get into `if` case.

```
if (sa_get_gsm_size() > 0)
   return sa_get_gsm_base() - sa_get_tseg_base();
else
   return CONFIG_SMM_TSEG_SIZE;
```