AMD: prograge guest MTRR values to nested page tables

Description:

Propagate the value in the guest MTRRs into the cache attributes for the AMD nested page tables, so that guest MTRRs have effect on the cache attributes, see:

https://lore.kernel.org/xen-devel/82fb70ca-25cf-6e06-968d-416798f65f79@suse.com/

And the AMD PM vol2 section "15.25.8 Combining Memory Types, MTRRs".

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information