sh: Use def_bool where possible.

Change occurances of:
	bool
	default X

to:
	def_bool X

Change ocurances of:
	bool "Foo"
	default X

to:
	def_bool X
	prompt "Foo"

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>