rt_ssize_t can give negative error code, which follows the unix style correctly
1. Add NUC980 Chili board supporting. 2. Correct NuMicro.h including. 3. Implement rt_hw_us_delay system call function. 4. Move board.c to drv_common.c for M480 and M2354 series.
1. Add NuMaker-M2354 BSP. 2. Fix SLCD library and modify its demo.