On branch llh_kernel-1.4
Changes to be committed:
	modified:   Makefile
	modified:   kernel.ld
	modified:   kernel/bin.S
	modified:   kernel/exec.c
	new file:   kernel/include/error.h
	modified:   kernel/include/memlayout.h
	modified:   kernel/include/proc.h
	modified:   kernel/include/timer.h
	modified:   kernel/include/trap.h
	modified:   kernel/main.c
	modified:   kernel/pipe.c
	modified:   kernel/proc.c
	new file:   kernel/sdcard.img
	modified:   kernel/sddata.S
	modified:   kernel/signal.c
	modified:   kernel/syscall.c
	modified:   kernel/sysfile.c
	modified:   kernel/sysproc.c
	modified:   kernel/syssig.c
	new file:   kernel/systime.c
	modified:   kernel/timer.c
	modified:   kernel/trap.c
	modified:   user/initcode.S

On branch llh_kernel-1.4
Changes to be committed:
	modified:   kernel.ld
	modified:   kernel/trap.c
	modified:   kernel/uservec.S

完善了loongarchregs.h与loongarch.h文件，完成了entry.S到main.c的启动，初步修改了ld与makefile文件。已经是一个能编译的项目。理论上能在模拟器上跑了。以后的修改可以在此基础上进行