m68k: Remove redundant 'default n' from Kconfig

'default n' is the default value for any bool or tristate Kconfig
setting so there is no need to write it explicitly.

Also since commit f467c564 ("kconfig: only write '# CONFIG_FOO
is not set' for visible symbols") the Kconfig behavior is the same
regardless of 'default n' being present or not:

    ...
    One side effect of (and the main motivation for) this change is making
    the following two definitions behave exactly the same:

        config FOO
                bool

        config FOO
                bool
                default n

    With this change, neither of these will generate a
    '# CONFIG_FOO is not set' line (assuming FOO isn't selected/implied).
    That might make it clearer to people that a bare 'default n' is
    redundant.
    ...
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig.machine

@@ -317,7 +317,6 @@ config UBOOT
 	help
 	  If you say Y here kernel will try to collect command
 	  line parameters from the initial u-boot stack.
-	default n
 
 config 4KSTACKS
 	bool "Use 4Kb for kernel stacks instead of 8Kb"
@@ -395,7 +394,6 @@ comment "ROM configuration"
 
 config ROM
 	bool "Specify ROM linker regions"
-	default n
 	help
 	  Define a ROM region for the linker script. This creates a kernel
 	  that can be stored in flash, with possibly the text, and data