m68k/amiga: Fix "debug=mem"

`debug=mem' on Amiga has been broken for a while.
early_param() processing is done very/too early, i.e. before
amiga_identify() / amiga_chip_init(), causing amiga_savekmsg_setup() not
to find any Chip RAM.

As we don't plan to free this memory anyway, just steal it from the initial
Chip RAM memory block instead.
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/amiga/config.c

@@ -610,17 +610,17 @@ static void amiga_mem_console_write(struct console *co, const char *s,
 
 static int __init amiga_savekmsg_setup(char *arg)
 {
-	static struct resource debug_res = { .name = "Debug" };
-
 	if (!MACH_IS_AMIGA || strcmp(arg, "mem"))
-		goto done;
+		return 0;
 
-	if (!AMIGAHW_PRESENT(CHIP_RAM)) {
-		printk("Warning: no chipram present for debugging\n");
-		goto done;
+	if (amiga_chip_size < SAVEKMSG_MAXMEM) {
+		pr_err("Not enough chipram for debugging\n");
+		return -ENOMEM;
 	}
 
-	savekmsg = amiga_chip_alloc_res(SAVEKMSG_MAXMEM, &debug_res);
+	/* Just steal the block, the chipram allocator isn't functional yet */
+	amiga_chip_size -= SAVEKMSG_MAXMEM;
+	savekmsg = (void *)ZTWO_VADDR(CHIP_PHYSADDR + amiga_chip_size);
 	savekmsg->magic1 = SAVEKMSG_MAGIC1;
 	savekmsg->magic2 = SAVEKMSG_MAGIC2;
 	savekmsg->magicptr = ZTWO_PADDR(savekmsg);
@@ -628,8 +628,6 @@ static int __init amiga_savekmsg_setup(char *arg)
 
 	amiga_console_driver.write = amiga_mem_console_write;
 	register_console(&amiga_console_driver);
-
-done:
 	return 0;
 }