MIPS: Add detection of DSP ASE Revision 2.

[ralf@linux-mips.org: This patch really only detects the ASE and passes its
existence on to userland via /proc/cpuinfo.  The DSP ASE Rev 2. adds new
resources but no resources that would need management by the kernel.]

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/4165/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>