m68k: Revive lost DIO bus config option

commit 0e152d80507b75c00aac60f2ffc586360687cd52 ("m68k: reorganize Kconfig
options to improve mmu/non-mmu selections") accidentally dropped the DIO
bus config option. Re-add it to the "Bus support" section.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig.bus

@@ -2,6 +2,15 @@ if MMU
 
 comment "Bus Support"
 
+config DIO
+	bool "DIO bus support"
+	depends on HP300
+	default y
+	help
+	  Say Y here to enable support for the "DIO" expansion bus used in
+	  HP300 machines. If you are using such a system you almost certainly
+	  want this.
+
 config NUBUS
 	bool
 	depends on MAC