KVM: arm64: Fix S1/S2 combination when FWB==1 and S2 has Device memory type

KVM: arm64: Fix S1/S2 combination when FWB==1 and S2 has Device memory type

The G.a revision of the ARM ARM had it pretty clear that HCR_EL2.FWB
had no influence on "The way that stage 1 memory types and attributes
are combined with stage 2 Device type and attributes." (D5.5.5).

However, this wording was lost in further revisions of the architecture.

Restore the intended behaviour, which is to take the strongest memory
type of S1 and S2 in this case, as if FWB was 0. The specification is
being fixed accordingly.

Fixes: be04cebf3e788 ("KVM: arm64: nv: Add emulation of AT S12E{0,1}{R,W}")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241125094756.609590-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>