x86: fix section mismatch for i386 init code

Startup code for i386 in arch/x86/kernel/head_32.S is using the
reference variable initial_code that is located in the .cpuinit.data
section. If CONFIG_HOTPLUG_CPU is enabled, startup code is not in an
init section and can be called later too. In this case the reference
initial_code must be kept too. This patch fixes this. See below for
the section mismatch warning.

 WARNING: vmlinux.o(.cpuinit.data+0x0): Section mismatch in reference
 from the variable initial_code to the function
 .init.text:i386_start_kernel()
 The variable __cpuinitdata initial_code references
 a function __init i386_start_kernel().
 If i386_start_kernel is only used by initial_code then
 annotate i386_start_kernel with a matching annotation.

Signed-off-by: Robert Richter <robert.richter@amd.com>
LKML-Reference: <1248716632-26844-1-git-send-email-robert.richter@amd.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>