MIPS: Kconfig and Makefile update for Netlogic XLR/XLS

Add NLM_XLR_BOARD, CPU_XLR and other config options
Makefile updates, mostly based on r4k

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2334/


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