MIPS: pgtable-bits: Define the CCA bit for WC writes on Ingenic cores

Ingenic uses the CCA:1 bit to achieve write-combine memory writes.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7401/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>