move processor initialization code into the function cpu_init

arch/x86/kernel/entry.asm

@@ -64,6 +64,21 @@ ALIGN 4
 stublet:
 ; initialize stack pointer.
     mov esp, default_stack_pointer
+; initialize cpu features
+    call cpu_init
+; interpret multiboot information
+    extern multiboot_init
+    push ebx
+    call multiboot_init
+    add esp, 4
+
+; jump to the boot processors's C code
+    extern main
+    call main
+    jmp $
+
+global cpu_init
+cpu_init:
     mov eax, cr0
 ; enable caching, disable paging and fpu emulation
     and eax, 0x1ffffffb
@@ -77,16 +92,7 @@ stublet:
     mov eax, cr4
     and eax, 0xfffbf9ff
     mov cr4, eax
-; interpret multiboot information
-    extern multiboot_init
-    push ebx
-    call multiboot_init
-    add esp, 4
-
-; jump to the boot processors's C code
-    extern main
-    call main
-    jmp $
+    ret
 
 ; This will set up our new segment registers. We need to do
 ; something special in order to set CS. We do what is called a