realtek: align declaration/static/extern function definitions for startup code

In 2023 upstream has tightened compiler checks with this patch
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit
/scripts/Makefile.extrawarn?h=v6.15&id=0fcb70851fbfea1776ae62f67c503fef8f0292b9

A consistent function definition is now needed. I.e.

- functions must be either declared with "static" or
- functions need an additional declaration (in the header file)

Before upgrading the Realtek target to 6.12 clean the code so that the main
6.12 PR can focus on real issues from the version bump.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/18925
Signed-off-by: Robert Marko <robimarko@gmail.com>

target/linux/realtek/files-6.6/arch/mips/rtl838x/prom.c

@@ -19,6 +19,7 @@
 #include <asm/page.h>
 #include <asm/cpu.h>
 #include <asm/fw/fw.h>
+#include <asm/prom.h>
 #include <asm/smp-ops.h>
 #include <asm/mips-cps.h>
 
@@ -95,7 +96,7 @@ void __init device_tree_init(void)
 	register_up_smp_ops();
 }
 
-void __init identify_rtl9302(void)
+static void __init identify_rtl9302(void)
 {
 	switch (sw_r32(RTL93XX_MODEL_NAME_INFO) & 0xfffffff0) {
 	case 0x93020810:

target/linux/realtek/files-6.6/arch/mips/rtl838x/setup.c

@@ -46,7 +46,7 @@ void __init plat_mem_setup(void)
 	__dt_setup_arch(dtb);
 }
 
-void plat_time_init_fallback(void)
+static void plat_time_init_fallback(void)
 {
 	struct device_node *np;
 	u32 freq = 500000000;