separate source into kernel/ user/ mkfs/

entry.S

@@ -1,25 +0,0 @@
-	# qemu -kernel starts at 0x1000. the instructions
-        # there seem to be provided by qemu, as if it
-        # were a ROM. the code at 0x1000 jumps to
-        # 0x8000000, the _start function here,
-        # in machine mode.
-.section .data
-.globl stack0
-.section .text
-.globl mstart
-.section .text
-.globl _entry
-_entry:
-	# set up a stack for C.
-        # stack0 is declared in start,
-        # with 4096 bytes per CPU.
-        la sp, stack0
-        li a0, 1024*4
-	csrr a1, mhartid
-        addi a1, a1, 1
-        mul a0, a0, a1
-        add sp, sp, a0
-	# jump to mstart() in start.c
-        call mstart
-junk:
-        j junk