arm64: KVM: Drop hyp_alternate_select for checking for ARM64_WORKAROUND_834220

There is no reason for using hyp_alternate_select when checking
for ARM64_WORKAROUND_834220, as each of the capabilities is
also backed by a static key. Just replace the KVM-specific
construct with cpus_have_const_cap(ARM64_WORKAROUND_834220).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>