ANDROID: KVM: arm64: pkvm: Don't access kvm_arm_hyp_percpu_base at EL1

The host KVM PMU code can currently index kvm_arm_hyp_percpu_base[]
through this_cpu_ptr_hyp_sym(), but will not actually dereference that
pointer when protected KVM is enabled. In preparation for making
kvm_arm_hyp_percpu_base[] unaccessible to the host, let's make sure the
indexing in hyp per-cpu pages is also done after the static key check to
avoid spurious accesses to EL2-private data from EL1.

Signed-off-by: Quentin Perret <qperret@google.com>
Bug: 225169428
Change-Id: I3f4e3f7ee789c31a1ae1f67e07edf8fb34f520b9