Add support for the following missing priviledged intructions:

For SH4:
- stc sgr, Rn
- stc.l sgr, @-Rn

For SH4A:
- ldc Rm, sgr
- ldc.l @Rm+, sgr
Signed-off-by: NAlexandre Courbot <gnurou@gmail.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>