target-mips: add missing check_dspr2 for multiply instructions

The emulator needs to check in hflags if DSP unit has been turned off before
it generates code for MUL_PH, MUL_S_PH, MULQ_S_W, and MULQ_RS_W.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
target-mips: fix incorrect behaviour for INSV

Corner case for INSV instruction when size=32 has not been correctly
implemented. The mask for size should be one bit wider, and preparing the
filter variable should be aware of this case too.

The test for INSV has been extended to include the case that triggers the
bug.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>