m68k: mvme16x: Add and use "mvme16x.h"

When building with W=1:

arch/m68k/mvme16x/config.c:208:6: warning: no previous prototype for ‘mvme16x_cons_write’ [-Wmissing-prototypes]
208 | void mvme16x_cons_write(struct console *co, const char *str, unsigned count)
| ^~~~~~~~~~~~~~~~~~

Fix this by introducing a new header file "mvme16x.h" for holding the
prototypes of functions implemented in arch/m68k/mvme16x/.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/6200cc3b26fad215c4524748af04692e38c5ecd2.1694613528.git.geert@linux-m68k.org

m68knommu: remove obsolete 68360 support

Remove the obsolete Motorola/Freescale 68360 SoC support. It has been
bit rotting for many years with little active use in mainlne. There has
been no serial driver support for many years, so it is largely not
useful in its current state.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>

m68k/mvme16x: Adopt common boot console

In a multi-platform kernel binary we only need one early console instance.

The difficulty here is that the common early console is started by
early_param(), whereas the MVME16x instance is started later by
config_mvme16x(). That means some interrupt setup must be done earlier.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stephen N Chivers <schivers@csc.com.au>
[Geert] Tag debug_cons_write() with __ref to kill section mismatch warning
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

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>