package/bluez5_utils: make tools optional

package/bluez5_utils: make tools optional

The tools are currently always build and installed. In many cases
those tools are not needed in a production system. So make this
step optional. This saves up to 2MB on the target.

Further tweak the deprecated option. It has effects when the --enable-tools
is set as well as when --enable-client is set. So explain this in the
options description and update the install step for gatttool to only be
added when client is enabled.

Signed-off-by: Michael Nosthoff <buildroot@heine.tech>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>