KVM: arm64: Simplify integration of adjust_nested_*_perms()

KVM: arm64: Simplify integration of adjust_nested_*_perms()

Instead of passing pointers to adjust_nested_*_perms(), allow
them to return a new set of permissions.

With some careful moving around so that the canonical permissions
are computed before the nested ones are applied, we end-up with
a bit less code, and something a bit more readable.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>