target/mips: Update some CP0 registers bit definitions

Update CP0 registers Config0, Config1, Config2, Config3,
Config4, and Config5 bit definitions.

Some of these bits will be utilized by upcoming nanoMIPS changes.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>