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

Commit 86c0baf123 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/vmlinux.lds.S

@@ -23,11 +23,15 @@ SECTIONS
 #else
 	. = PAGE_OFFSET + TEXT_OFFSET;
 #endif
-	.init : {			/* Init code and data		*/
+	.text.head : {
 		_stext = .;
-			_sinittext = .;
+		_sinittext = .;
+		*(.text.head)
+	}
+
+	.init : {			/* Init code and data		*/
 			*(.init.text)
-			_einittext = .;
+		_einittext = .;
 		__proc_info_begin = .;
 			*(.proc.info.init)
 		__proc_info_end = .;