MIPS: Advertise MIPSr6 via HWCAP when appropriate

MIPS: Advertise MIPSr6 via HWCAP when appropriate

When running on a CPU implementing the release 6 of the MIPS32 or MIPS64
ISA, advertise that to userland via the appropriate HWCAP bit.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-kernel@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/10798/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>