libx264: Blacklist all MIPS CPUs for assembly optimizations
None of the CPUs supported in OpenWrt/LEDE are MSA capable (requires
MIPS32r5/r6 for that) which would lead to this error during configure:
You specified a pre-MSA CPU in your CFLAGS.
If you really want to run on such a CPU, configure with --disable-asm.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>