board: enable FPU for nsim_sem_mpu and update mdb.args

Enable FPU for nsim_sem_mpu_stack_guard to fix zdsp.basicmath.fpu
failure due to lack of FPU option. Add FPU feature to its related
mdb.args, also for nsim_sem and nsim_em7d_v22 boards.

Signed-off-by: Siyuan Cheng <siyuanc@synopsys.com>