arch/m68k: add 68000 nommu support

Everyone thinks they like ARM but secretly they want to run
Linux on their Megadrive[0].

Building a working toolchain/userland for nommu m68k is a bit
difficult because of the bitrotten tools all over the place and
one big issue is GCC generates code that uses unaligned
accesses that will cause an exception on 68000 machines if you
aren't careful.

Buildroot can easily create a working toolchain and userland
for nommu m68k so why not?

0 - This isn't a joke, I'm working on this. I have u-boot working
    on the Megadrive, Linux is already working on a bunch of 68000
    machines and I just need to get everything a little bit smaller
    to get into 4MB of RAM.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

arch/Config.in.m68k

@@ -23,6 +23,11 @@ choice
 	help
 	  Specific CPU variant to use
 
+config BR2_m68k_68000
+	bool "68000"
+	select BR2_m68k_m68k
+	select BR2_SOFT_FLOAT
+
 config BR2_m68k_68030
 	bool "68030"
 	select BR2_m68k_m68k
@@ -41,6 +46,7 @@ config BR2_m68k_cf5208
 endchoice
 
 config BR2_GCC_TARGET_CPU
+	default "68000"		if BR2_m68k_68000
 	default "68030"		if BR2_m68k_68030
 	default "68040"		if BR2_m68k_68040
 	default "5208"		if BR2_m68k_cf5208