xtensa: make startup code discardable

Move it from .text to .init.text to get rid of it after boot and
prevent illegal section references.
Signed-off-by: NDaniel Glöckner <dg@emlix.com>
Signed-off-by: NChris Zankel <chris@zankel.net>

arch/xtensa/kernel/head.S

@@ -53,7 +53,7 @@ _start:	_j	2f
 2:	l32r	a0, 1b
 	jx	a0
 
-	.text
+	.section .init.text, "ax"
 	.align 4
 _startup: