MIPS: Netlogic: Exclude netlogic,xlp-pic code from XLR builds

MIPS: Netlogic: Exclude netlogic,xlp-pic code from XLR builds

Code in arch/mips/netlogic/common/irq.c which handles the XLP PIC fails
to build in XLR configurations due to cpu_is_xlp9xx not being defined,
leading to the following build failure:

    arch/mips/netlogic/common/irq.c: In function ‘xlp_of_pic_init’:
    arch/mips/netlogic/common/irq.c:298:2: error: implicit declaration
    of function ‘cpu_is_xlp9xx’ [-Werror=implicit-function-declaration]
      if (cpu_is_xlp9xx()) {
      ^

Although the code was conditional upon CONFIG_OF which is indirectly
selected by CONFIG_NLM_XLP_BOARD but not CONFIG_NLM_XLR_BOARD, the
failing XLR with CONFIG_OF configuration can be configured manually or
by randconfig.

Fix the build failure by making the affected XLP PIC code conditional
upon CONFIG_CPU_XLP which is used to guard the inclusion of
asm/netlogic/xlp-hal/xlp.h that provides the required cpu_is_xlp9xx
function.

[ralf@linux-mips.org: Fixed up as per Jayachandran's suggestion.]

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14524/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>