m68k/mac: Make CONFIG_HEARTBEAT unavailable on Mac

mac_heartbeat() was never really implemented.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/Kconfig.devices

@@ -8,8 +8,8 @@ config ARCH_MAY_HAVE_PC_FDC
 menu "Platform devices"
 
 config HEARTBEAT
-	bool "Use power LED as a heartbeat" if AMIGA || APOLLO || ATARI || MAC ||Q40
-	default y if !AMIGA && !APOLLO && !ATARI && !MAC && !Q40 && HP300
+	bool "Use power LED as a heartbeat" if AMIGA || APOLLO || ATARI || Q40
+	default y if !AMIGA && !APOLLO && !ATARI && !Q40 && HP300
 	help
 	  Use the power-on LED on your machine as a load meter.  The exact
 	  behavior is platform-dependent, but normally the flash frequency is