ANDROID: KVM: arm64: Fix vcpu sys_reg accessors when running with VHE

Commit 3f653641 ("ANDROID: KVM: arm64: refactor vcpu_read_sys_reg
and vcpu_write_sys_reg for hyp use") predicated direct access to the
live vCPU registers on an is_vhe_hyp_code() check, neglecting the fact
that these functions are also used by the VHE *kernel* code.

Restore the old behaviour by changing the check so that only the nVHE
hyp code unconditionally uses the 'ctxt_sys_reg' table.

Reported-by: Marc Zyngier <mzyngier@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Bug: 209580772
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I17d4c12ffdbbd95e8e8d1820ebb6438b138361aa