powerpc: Mark probe_machine() __init and static

Prior to commit b1923caa ("powerpc: Merge 32-bit and 64-bit
setup_arch()") probe_machine() was called from setup_32/64.c and lived
in setup-common.c. But now it's only called from setup-common.c so it
can be static and __init, and we don't need the declaration in
machdep.h either.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211124093254.1054750-6-mpe@ellerman.id.au

arch/powerpc/include/asm/machdep.h

@@ -235,8 +235,6 @@ extern struct machdep_calls *machine_id;
 		machine_id == &mach_##name; \
 	})
 
-extern void probe_machine(void);
-
 #ifdef CONFIG_PPC_PMAC
 /*
  * Power macintoshes have either a CUDA, PMU or SMU controlling

arch/powerpc/kernel/setup-common.c

@@ -582,7 +582,7 @@ static __init int add_pcspkr(void)
 device_initcall(add_pcspkr);
 #endif	/* CONFIG_PCSPKR_PLATFORM */
 
-void probe_machine(void)
+static __init void probe_machine(void)
 {
 	extern struct machdep_calls __machine_desc_start;
 	extern struct machdep_calls __machine_desc_end;