MIPS: kernel: traps: Add MIPS R6 related definitions

Add MIPS R6 support to cache and ftlb exceptions, as well as
to the hwrena and ebase register configuration.

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>