linux-user/loongarch64: Decode BRK break codes for FPE signals

linux-user/loongarch64: Decode BRK break codes for FPE signals

Handle specific LoongArch BRK break codes in user-mode emulation
to deliver accurate floating-point exception signals. Specifically,
BRK_OVERFLOW (6) triggers TARGET_FPE_INTOVF, and BRK_DIVZERO (7)
triggers TARGET_FPE_INTDIV. Other BRK codes fall back to a generic
SIGTRAP.

This improves correctness for programs that rely on BRK to signal
overflow or divide-by-zero conditions.

Signed-off-by: WANG Rui <wangrui@loongson.cn>
Acked-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20250414074952.6253-1-wangrui@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>