[ARM] Ensure head text is always placed at the start of kernel

Commit 86c0baf123e474b6eb404798926ecf62b426bf3a highlighted that we
may end up with the head text placed elsewhere in the kernel image.
Introduce a new .text.head section to contain the initial kernel
startup code, and always place this section at the beginning of the
kernel image.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/head-nommu.S

@@ -33,7 +33,7 @@
  * numbers for r1.
  *
  */
-	__INIT
+	.section ".text.head", "ax"
 	.type	stext, %function
 ENTRY(stext)
 	msr	cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE @ ensure svc mode

arch/arm/kernel/head.S

@@ -73,7 +73,7 @@
  * crap here - that's what the boot loader (or in extreme, well justified
  * circumstances, zImage) is for.
  */
-	__INIT
+	.section ".text.head", "ax"
 	.type	stext, %function
 ENTRY(stext)
 	msr	cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE @ ensure svc mode

arch/arm/kernel/vmlinux.lds.S

@@ -23,9 +23,13 @@ SECTIONS
 #else
 	. = PAGE_OFFSET + TEXT_OFFSET;
 #endif
-	.init : {			/* Init code and data		*/
+	.text.head : {
 		_stext = .;
 		_sinittext = .;
+		*(.text.head)
+	}
+
+	.init : {			/* Init code and data		*/
 			*(.init.text)
 		_einittext = .;
 		__proc_info_begin = .;