powerpc/kdump: Fix powernv build break when KEXEC_CORE=n

If KEXEC_CORE is not enabled, powernv builds fail as follows.

  arch/powerpc/platforms/powernv/smp.c: In function 'pnv_smp_cpu_kill_self':
  arch/powerpc/platforms/powernv/smp.c:236:4: error:
  	implicit declaration of function 'crash_ipi_callback'

Add dummy function calls, similar to kdump_in_progress(), to solve the
problem.

Fixes: 4145f358644b ("powernv/kdump: Fix cases where the kdump kernel can get HMI's")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/kexec.h

@@ -140,6 +140,12 @@ static inline bool kdump_in_progress(void)
 	return false;
 }
 
+static inline void crash_ipi_callback(struct pt_regs *regs) { }
+
+static inline void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *))
+{
+}
+
 #endif /* CONFIG_KEXEC_CORE */
 #endif /* ! __ASSEMBLY__ */
 #endif /* __KERNEL__ */