Add missing init section definitions

When adding __devinitconst etc. the __initconst variant
were missed.
Add this one and proper definitions for .head.text for use
in .S files.
The naming .head.text is preferred over .text.head as the
latter will conflict for a function named head when introducing
-ffunctions-sections.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

include/asm-generic/vmlinux.lds.h

@@ -238,6 +238,9 @@
 		*(.kprobes.text)					\
 		VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
+/* Section used for early init (in .S files) */
+#define HEAD_TEXT  *(.head.text)
+
 /* init and exit section handling */
 #define INIT_DATA							\
 	*(.init.data)							\