KVM: arm64: Mark the host stage-2 memory pools static

The host stage-2 memory pools are not used outside of mem_protect.c,
mark them static.

Fixes: 1025c8c0 ("KVM: arm64: Wrap the host with a stage 2")
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NQuentin Perret <qperret@google.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210514085640.3917886-3-qperret@google.com

arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -23,8 +23,8 @@
 extern unsigned long hyp_nr_cpus;
 struct host_kvm host_kvm;
 
-struct hyp_pool host_s2_mem;
-struct hyp_pool host_s2_dev;
+static struct hyp_pool host_s2_mem;
+static struct hyp_pool host_s2_dev;
 
 /*
  * Copies of the host's CPU features registers holding sanitized values.