target-mips: fix DSP overflow macro and affected routines

The previous implementation incorrectly used same macro to detect overflow
for addition and subtraction. This patch makes distinction between these
two, and creates separate macros. The affected routines are changed
accordingly.

This change also includes additions to the existing tests for SUBQ_S_PH and
SUBQ_S_W that would trigger the fixed issue, and it removes dead code from
the test file. The last test case in subq_s_w.c is a bug found/reported/
isolated by Klaus Peichl from Dolby.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
target-mips: Translate breaks and traps into the appropriate signal

GCC and GAS are capable of generating traps or breaks to check for
division by zero.  Additionally, GAS is capable of generating traps
or breaks to check for overflow on certain division and multiplication
operations.  The Linux kernel translates these traps and breaks into
signals.  This patch implements the corresponding feature in QEMU.

Signed-off-by: Meador Inge <meadori@codesourcery.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>