KVM: arm64: Don't constrain maximum IPA size based on host configuration

Now that the guest stage-2 page-tables are managed independently from
the host stage-1 page-tables, we can avoid constraining the IPA size
based on the host and instead limit it only based on the PARange field
of the ID_AA64MMFR0 register.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20200911132529.19844-22-will@kernel.org