KVM: x86: apply guest MTRR virtualization on host reserved pages

KVM: x86: apply guest MTRR virtualization on host reserved pages

Currently guest MTRR is avoided if kvm_is_reserved_pfn returns true.
However, the guest could prefer a different page type than UC for
such pages. A good example is that pass-throughed VGA frame buffer is
not always UC as host expected.

This patch enables full use of virtual guest MTRRs.

Suggested-by: Xiao Guangrong <[email protected]>
Tested-by: Joerg Roedel <[email protected]> (on AMD)
Signed-off-by: Paolo Bonzini <[email protected]>