x86: fix cpu hotplug on 32bit

commit 3e9704739daf46a8ba6593d749c67b5f7cd633d2 ("x86: boot secondary
cpus through initial_code") causes the kernel to crash when a CPU is
brought online after the read only sections have been write
protected. The write to initial_code in do_boot_cpu() fails.

Move inital_code to .cpuinit.data section.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/head_32.S

@@ -456,9 +456,6 @@ is386:	movl $2,%ecx		# set MP
 1:
 #endif /* CONFIG_SMP */
 	jmp *(initial_code)
-.align 4
-ENTRY(initial_code)
-	.long i386_start_kernel
 
 /*
  * We depend on ET to be correct. This checks for 287/387.
@@ -601,6 +598,11 @@ ignore_int:
 #endif
 	iret
 
+.section .cpuinit.data,"wa"
+.align 4
+ENTRY(initial_code)
+	.long i386_start_kernel
+
 .section .text
 /*
  * Real beginning of normal "text" segment