sh: Move entry point code to .text.head.

Follow Al Viro's m68k change from l-k:

	i.e. tell modpost that entry point code (that has to be outside
	of .init.text for external reasons) is OK to refer to .init.*

Shuts up some section mismatch warnings from modpost.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>