powerpc: Fix Section mismatch warnings in prom_init.c

This patches tries to fix a couple of Section mismatch warnings like
following one:

WARNING: arch/powerpc/kernel/built-in.o(.text+0x2923c): Section mismatch
in reference from the function .prom_query_opal() to the
function .init.text:.call_prom()
The function .prom_query_opal() references
the function __init .call_prom().
This is often because .prom_query_opal lacks a __init
annotation or the annotation of .call_prom is wrong.
Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/prom_init.c

@@ -1312,7 +1312,7 @@ static struct opal_secondary_data {
 
 extern char opal_secondary_entry;
 
-static void prom_query_opal(void)
+static void __init prom_query_opal(void)
 {
 	long rc;
 
@@ -1436,7 +1436,7 @@ static void __init prom_opal_hold_cpus(void)
 	prom_debug("prom_opal_hold_cpus: end...\n");
 }
 
-static void prom_opal_takeover(void)
+static void __init prom_opal_takeover(void)
 {
 	struct opal_secondary_data *data = &RELOC(opal_secondary_data);
 	struct opal_takeover_args *args = &data->args;