powerpc: Fix section mismatch warning in smp_setup_pacas()

Section mismatch in reference from the function .smp_setup_pacas() to
the function .init.text:.allocate_paca()

The only caller of smp_setup_pacas() is setup_arch() which is __init,
so mark smp_setup_pacas() __init.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210314093333.132657-1-mpe@ellerman.id.au

arch/powerpc/kernel/setup-common.c

@@ -828,7 +828,7 @@ static __init void print_system_info(void)
 }
 
 #ifdef CONFIG_SMP
-static void smp_setup_pacas(void)
+static void __init smp_setup_pacas(void)
 {
 	int cpu;