m68k: Sort selects in main Kconfig

Sort the list of select statements in the main Kconfig file for the m68k
architecture, to avoid conflicts when modifying this list.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20200826125259.24069-1-geert@linux-m68k.org