KVM: PPC: Book3S HV: Declare some prototypes

This fixes these W=1 compile errors:

../arch/powerpc/kvm/book3s_hv_builtin.c:425:6: error: no previous prototype for ‘kvmppc_read_intr’ [-Werror=missing-prototypes]
  425 | long kvmppc_read_intr(void)
      |      ^~~~~~~~~~~~~~~~
../arch/powerpc/kvm/book3s_hv_builtin.c:652:6: error: no previous prototype for ‘kvmppc_bad_interrupt’ [-Werror=missing-prototypes]
  652 | void kvmppc_bad_interrupt(struct pt_regs *regs)
      |      ^~~~~~~~~~~~~~~~~~~~
../arch/powerpc/kvm/book3s_hv_builtin.c:695:6: error: no previous prototype for ‘kvmhv_p9_set_lpcr’ [-Werror=missing-prototypes]
  695 | void kvmhv_p9_set_lpcr(struct kvm_split_mode *sip)
      |      ^~~~~~~~~~~~~~~~~
../arch/powerpc/kvm/book3s_hv_builtin.c:740:6: error: no previous prototype for ‘kvmhv_p9_restore_lpcr’ [-Werror=missing-prototypes]
  740 | void kvmhv_p9_restore_lpcr(struct kvm_split_mode *sip)
      |      ^~~~~~~~~~~~~~~~~~~~~
../arch/powerpc/kvm/book3s_hv_builtin.c:768:6: error: no previous prototype for ‘kvmppc_set_msr_hv’ [-Werror=missing-prototypes]
  768 | void kvmppc_set_msr_hv(struct kvm_vcpu *vcpu, u64 msr)
      |      ^~~~~~~~~~~~~~~~~
../arch/powerpc/kvm/book3s_hv_builtin.c:817:6: error: no previous prototype for ‘kvmppc_inject_interrupt_hv’ [-Werror=missing-prototypes]
  817 | void kvmppc_inject_interrupt_hv(struct kvm_vcpu *vcpu, int vec, u64 srr1_flags)
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210104143206.695198-21-clg@kaod.org

arch/powerpc/include/asm/kvm_book3s.h

@@ -277,6 +277,13 @@ extern int kvmppc_hcall_impl_hv_realmode(unsigned long cmd);
 extern void kvmppc_copy_to_svcpu(struct kvm_vcpu *vcpu);
 extern void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu);
 
+long kvmppc_read_intr(void);
+void kvmppc_bad_interrupt(struct pt_regs *regs);
+void kvmhv_p9_set_lpcr(struct kvm_split_mode *sip);
+void kvmhv_p9_restore_lpcr(struct kvm_split_mode *sip);
+void kvmppc_set_msr_hv(struct kvm_vcpu *vcpu, u64 msr);
+void kvmppc_inject_interrupt_hv(struct kvm_vcpu *vcpu, int vec, u64 srr1_flags);
+
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 void kvmppc_save_tm_pr(struct kvm_vcpu *vcpu);
 void kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu);