Use C99 'bool' rather than Machish 'boolean_t'.

Requested by:	jhb
Re-enable CTL in GENERIC on i386 and amd64, but turn on the CTL disable
tunable by default.

This will allow GENERIC configurations to boot on small memory boxes, but
not require end users who want to use CTL to recompile their kernel.  They
can simply set kern.cam.ctl.disable=0 in loader.conf.

The eventual solution to the memory usage problem is to change the way
CTL allocates memory to be more configurable, but this should fix things
for small memory situations in the mean time.

UPDATING:		Explain the change in the CTL configuration, and
			how users can enable CTL if they would like to use
			it.

sys/conf/options:	Add a new option, CTL_DISABLE, that prevents CTL
			from initializing.

ctl.c:			If CTL_DISABLE is turned on, don't initialize.

i386/conf/GENERIC,
amd64/conf/GENERIC:	Re-enable device ctl, and add the CTL_DISABLE
			option.
Add quirk to enable headphones redirection on Lenovo X220.

PR:		kern/174876
MFC after:	1 week