x86: 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"

Shows no difference in generated config for allmodconfig/allyesconfig.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>