MIPS: Netlogic: Add support for XLP2XX

XLP2XX is first in the series of 28nm XLPII processors.

The changes are to:
* Add processor ID for XLP2XX to asm/cpu.h and kernel/cpu-probe.c.
* Add a cpu_is_xlpii() function to check for XLPII processors.
* Update xlp_mmu_init() to use config4 to enable extended TLB.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5698/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>