MIPS: cevt-r4k: Use CAUSEF_TI, CAUSEF_PCI constants

Use CAUSEF_TI and CAUSEF_PCI constants from asm/mipsregs.h rather than
the magic values (1 << 30) and (1 << 26).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9124/


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