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: Daniel Glöckner <dg@emlix.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/arch/xtensa/kernel/head.S b/arch/xtensa/kernel/head.S
index d092c22..0817f9d 100644
--- a/arch/xtensa/kernel/head.S
+++ b/arch/xtensa/kernel/head.S
@@ -53,7 +53,7 @@
 2:	l32r	a0, 1b
 	jx	a0
 
-	.text
+	.section .init.text, "ax"
 	.align 4
 _startup: