boot_loader: add missing stubs

u_boot build still broken

Change-Id: Iba93ce7bf0d5c30a95ff98420a2e419eb28bb398
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2412
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

src/system/boot/platform/amiga_m68k/cpu.cpp

@@ -105,3 +105,9 @@ cpu_init()
 		// ...or not!
 }
 
+
+extern "C" void
+platform_load_ucode(BootVolume& volume)
+{
+}
+

src/system/boot/platform/atari_m68k/cpu.cpp

@@ -130,3 +130,9 @@ cpu_init()
 		// ...or not!
 }
 
+
+extern "C" void
+platform_load_ucode(BootVolume& volume)
+{
+}
+

src/system/boot/platform/openfirmware/Jamfile

@@ -12,6 +12,7 @@ UsePrivateHeaders [ FDirName graphics common ] ;
 }
 
 local platform_src =
+	cpu.cpp
 	console.cpp
 	debug.cpp
 	devices.cpp

src/system/boot/platform/openfirmware/cpu.cpp

@@ -0,0 +1,14 @@
+/*
+ * Copyright 2020, Jérôme Duval, jerome.duval@gmail.com. All rights reserved.
+ * Distributed under the terms of the MIT License.
+*/
+
+
+#include <boot/platform.h>
+
+
+extern "C" void
+platform_load_ucode(BootVolume& volume)
+{
+}
+

src/system/boot/platform/u-boot/cpu.cpp

@@ -36,3 +36,8 @@ cpu_init()
 		panic("You need a 6502 or higher in order to boot!\n");
 }
 
+
+extern "C" void
+platform_load_ucode(BootVolume& volume)
+{
+}