MIPS: dsp: Simplify the DSP macros.

Simplify the DSP macros for vanilla (non-microMIPS) kernels and
toolchains that do not support the DSP ASEs.

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Patchwork: http://patchwork.linux-mips.org/patch/4687/


Signed-off-by: John Crispin <blogic@openwrt.org>