MIPS: kernel: cps-vec: Replace 'la' macro with PTR_LA

MIPS: kernel: cps-vec: Replace 'la' macro with PTR_LA

The PTR_LA macro will pick the correct "la" or "dla" macro to
load an address to a register. This gets rids of the following
warnings (and others) when building a 64-bit CPS kernel:

arch/mips/kernel/cps-vec.S:63: Warning: la used to load 64-bit address
arch/mips/kernel/cps-vec.S:159: Warning: la used to load 64-bit address
arch/mips/kernel/cps-vec.S:220: Warning: la used to load 64-bit address
arch/mips/kernel/cps-vec.S:240: Warning: la used to load 64-bit address
[...]

Cc: <stable@vger.kernel.org> # 3.16+
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/10587/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>