KVM: arm64: Remove obsolete kvm_virt_to_phys abstraction

This abstraction was introduced to hide the difference between arm and
arm64 but, with the former no longer supported, this abstraction can be
removed and the canonical kernel API used directly instead.

Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
CC: Marc Zyngier <maz@kernel.org>
CC: James Morse <james.morse@arm.com>
CC: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20200519104036.259917-1-ascull@google.com