[S] Change in coreboot[master]: acpi: Add missing cbfs_unmap()

[Tim Van Patten (Code Review)]

Attention is currently required from: Lance Zhao, Konrad Adamczyk, Jakub Czapiga, Tim Wawrzynczak, Grzegorz Bernacki, Karthik Ramasubramanian.

Tim Van Patten has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74715 )

Change subject: acpi: Add missing cbfs_unmap()
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Patch Set 2:

(1 comment)

File src/acpi/acpi.c:

https://review.coreboot.org/c/coreboot/+/74715/comment/db262c16_bdcb2ce9 
PS2, Line 1934: 	cbfs_unmap(dsdt_file);
This call doesn't actually free the memory. Instead, these `cbfs_unmap()` calls need to be reversed, since the memory must be freed in reverse order of how it was allocated.

Looking at the implementation of `cbfs_unmap()`, it just calls `mem_pool_free()`:

`src/third_party/coreboot/src/lib/cbfs.c`
```
void cbfs_unmap(void *mapping)
{
...
    mem_pool_free(&cbfs_cache, mapping);
}
```

However, `mem_pool_free()` will only free the last allocation, which in this case was `slic_file`.

`src/third_party/coreboot/src/commonlib/mem_pool.c`
```
void mem_pool_free(struct mem_pool *mp, void *p)
{
    /* Determine if p was the most recent allocation. */
    if (p == NULL || mp->last_alloc != p)   <<---- last_alloc == slic_file
    	return;

mp->free_offset = mp->last_alloc - mp->buf;
    mp->last_alloc = mp->second_to_last_alloc;
    /* No way to track allocation before this one. */
    mp->second_to_last_alloc = NULL;
}
```