m68k: Multi-platform EARLY_PRINTK

Make the boot console available to more m68k platforms by leveraging
the head.S debug console.

The boot console is enabled by the "earlyprintk" command line argument
which is how most other architectures do this.

This is a change of behaviour for the Mac but does not negatively impact
the common use-case which is not debugging.

This is also a change of behaviour for other platforms because it means
the serial port stays quiet when CONFIG_EARLY_PRINTK is not enabled. This
is also an improvement for the common use-case.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stephen N Chivers <schivers@csc.com.au>
[Geert: CONSOLE_DEBUG should depend on CONFIG_FONT_SUPPORT]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig.debug

@@ -12,12 +12,17 @@ config BOOTPARAM_STRING
 
 config EARLY_PRINTK
 	bool "Early printk"
-	depends on MVME16x || MAC
+	depends on !(SUN3 || M68360 || M68000 || COLDFIRE)
 	help
           Write kernel log output directly to a serial port.
+          Where implemented, output goes to the framebuffer as well.
+          PROM console functionality on Sun 3x is not affected by this option.
+
+          Pass "earlyprintk" on the kernel command line to get a
+          boot console.
 
           This is useful for kernel debugging when your machine crashes very
-          early before the console code is initialized.
+          early, i.e. before the normal console driver is loaded.
           You should normally say N here, unless you want to debug such a crash.
 
 if !MMU