m68k: set a default value for MEMORY_RESERVE

m68k: set a default value for MEMORY_RESERVE

'make randconfig' can produce a .config file with
"CONFIG_MEMORY_RESERVE=" (no value) since it has no default.
When a subsequent 'make all' is done, kconfig restarts the config
and prompts for a value for MEMORY_RESERVE. This breaks
scripting/automation where there is no interactive user input.

Add a default value for MEMORY_RESERVE. (Any integer value will
work here for kconfig.)

Fixes a kconfig warning:

.config:214:warning: symbol value '' invalid for MEMORY_RESERVE
* Restart config...
Memory reservation (MiB) (MEMORY_RESERVE) [] (NEW)

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") # from beginning of git history
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>