arch-mips: Add MACHINEOVERRIDES variables to reduce duplication

arch-mips: Add MACHINEOVERRIDES variables to reduce duplication

In some cases, each MIPS variant in a recipe requires a duplicate
line. Even if the passed flag is the same.

Add global MACHINEOVERRIDES variables for the following
 * mipsarch		: All MIPS
 * mipsarch{eb,el}	: All MIPS Big/Little Endian
 * mipsarchr6		: All MIPS R6
 * mipsarcho32		: All MIPS o32 Endian Independent
 * mipsarchn32		: All MIPS n32 Endian Independent
 * mipsarchn64		: All MIPS n64 Endian Independent
 * mipsarcho32{eb,el}	: All MIPS o32 Big/Little Endian
 * mipsarchn32{eb,el}	: All MIPS n32 Big/Little Endian
 * mipsarchn64{eb,el}	: All MIPS n64 Big/Little Endian

This is intended to reduce duplications in recipes

[YOCTO #10404]

Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>