MIPS: ath79: get rid of some ifdefs in mach-ubnt-xm.c

Remove a superfluous ifdef around an include. Also
reorganize the board setup code a bit, so another
ifdef can be removed.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3497/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>