mips: Add macros for CP0.Config3 and CP0.Config4 bits

Define macros for CP0.Config3 and CP0.Config4 bits.  These used to be
exhaustive as at MIPS32r3, but more bits may have been added since.

Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
