MIPS: define bits introduced for hybrid FPRs

Add definitions for the FRE & UFE bits in Config5, and the FREP bit in
FPIR. These bits are used to support a hybrid FPR scheme allowing a
mixture of FP32 & FP64 code to execute within a task.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7674/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>