Change in coreboot[master]: timestamp,amd/common/apob_cache: Add timestamps for APOB

[Raul Rangel (Code Review)]

Attention is currently required from: Jason Glenesk, Marshall Dawson, Angel Pons, Karthik Ramasubramanian, Felix Held.
Raul Rangel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55401 )

Change subject: timestamp,amd/common/apob_cache: Add timestamps for APOB
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Patch Set 1:

(1 comment)

File src/soc/amd/common/block/apob/apob_cache.c:

https://review.coreboot.org/c/coreboot/+/55401/comment/fb3600aa_4845d134 
PS1, Line 143: timestamp_add_now(TS_AMD_APOB_ERASE_START);
             : 
             : 	/* write data to flash region */
             : 	if (rdev_eraseat(&write_rdev, 0, DEFAULT_MRC_CACHE_SIZE) < 0) {
             : 		printk(BIOS_ERR, "Error: APOB flash region erase failed\n");
             : 		return;
             : 	}
             : 
             : 	timestamp_add_now(TS_AMD_APOB_WRITE_START);
             : 
             : 	if (rdev_writeat(&write_rdev, apob_src_ram, 0, apob_src_ram->size) < 0) {
             : 		printk(BIOS_ERR, "Error: APOB flash region update failed\n");
             : 		return;
             : 	}
> Idea for another patch: If APOB changes are usually small, it may be a good idea to only rewrite the […]

I think the APOB data only really changes when we update firmware versions. Do we have existing code to calculate the diffs and only erase-update those blocks?