KVM: arm64: Rename HSR to ESR

kvm/arm32 isn't supported since commit 541ad015 ("arm: Remove
32bit KVM host support"). So HSR isn't meaningful since then. This
renames HSR to ESR accordingly. This shouldn't cause any functional
changes:

   * Rename kvm_vcpu_get_hsr() to kvm_vcpu_get_esr() to make the
     function names self-explanatory.
   * Rename variables from @hsr to @esr to make them self-explanatory.

Note that the renaming on uapi and tracepoint will cause ABI changes,
which we should avoid. Specificly, there are 4 related source files
in this regard:

   * arch/arm64/include/uapi/asm/kvm.h  (struct kvm_debug_exit_arch::hsr)
   * arch/arm64/kvm/handle_exit.c       (struct kvm_debug_exit_arch::hsr)
   * arch/arm64/kvm/trace_arm.h         (tracepoints)
   * arch/arm64/kvm/trace_handle_exit.h (tracepoints)

Signed-off-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Andrew Scull <ascull@google.com>
Link: https://lore.kernel.org/r/20200630015705.103366-1-gshan@redhat.com