powerpc/powermac: Move pmac_pfunc_base_install prototype to header file

The pmac_pfunc_base_install prototype was declared in powermac/smp.c since
function was used there, move it to pmac_pfunc.h header to be visible in
pfunc_base.c. Fix a warning treated as error with W=1:

  arch/powerpc/platforms/powermac/pfunc_base.c:330:12: error: no previous prototype for ‘pmac_pfunc_base_install’ [-Werror=missing-prototypes]
Suggested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/pmac_pfunc.h

@@ -245,6 +245,7 @@ extern void pmf_put_function(struct pmf_function *func);
 
 extern int pmf_call_one(struct pmf_function *func, struct pmf_args *args);
 
+int pmac_pfunc_base_install(void);
 
 /* Suspend/resume code called by via-pmu directly for now */
 extern void pmac_pfunc_base_suspend(void);

arch/powerpc/platforms/powermac/smp.c

@@ -65,7 +65,6 @@
 #endif
 
 extern void __secondary_start_pmac_0(void);
-extern int pmac_pfunc_base_install(void);
 
 static void (*pmac_tb_freeze)(int freeze);
 static u64 timebase;