[kernel] Improve the code comment of the cpu.c
[kernel] Improve the code comment of the cpu.c

geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread