[XTENSA] clean-up header files

The header files in the asm-xtensa directory are not clean and
'make headers_check' fails. This is a first patch to fix most of
the header files. It removes unnecessary include statements and
adds some that are required for building the kernel. The linker
script required some updates or the linking stage would fail.

Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/include/asm-xtensa/byteorder.h b/include/asm-xtensa/byteorder.h
index 0f540a5..765edf1 100644
--- a/include/asm-xtensa/byteorder.h
+++ b/include/asm-xtensa/byteorder.h
@@ -12,6 +12,7 @@
 #define _XTENSA_BYTEORDER_H
 
 #include <asm/types.h>
+#include <linux/compiler.h>
 
 static __inline__ __attribute_const__ __u32 ___arch__swab32(__u32 x)
 {
@@ -78,4 +79,4 @@
 # error processor byte order undefined!
 #endif
 
-#endif /* __ASM_XTENSA_BYTEORDER_H */
+#endif /* _XTENSA_BYTEORDER_H */