rockchip: transform rockchip_capsule_update_board_setup into a weak function symbol

There's only one user of rockchip_capsule_update_board_setup, which is
in board.c, and only one board defines it, so instead of having a header
only for one function symbol, let's just use a weak symbol instead.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>

arch/arm/include/asm/arch-rockchip/misc.h

@@ -1,9 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0+ */
-/*
- * RK3399: Architecture common definitions
- *
- * Copyright (C) 2019 Collabora Inc - https://www.collabora.com/
- *      Rohan Garg <rohan.garg@collabora.com>
- */
-
-void rockchip_capsule_update_board_setup(void);

arch/arm/mach-rockchip/board.c

@@ -32,7 +32,6 @@
 #include <asm/arch-rockchip/boot_mode.h>
 #include <asm/arch-rockchip/clock.h>
 #include <asm/arch-rockchip/periph.h>
-#include <asm/arch-rockchip/misc.h>
 #include <power/regulator.h>
 
 #if defined(CONFIG_EFI_HAVE_CAPSULE_SUPPORT) && defined(CONFIG_EFI_PARTITION)
@@ -148,6 +147,10 @@ void set_dfu_alt_info(char *interface, char *devstr)
 	env_set("dfu_alt_info", buf);
 }
 
+__weak void rockchip_capsule_update_board_setup(void)
+{
+}
+
 static void gpt_capsule_update_setup(void)
 {
 	int p, i, ret;