x11-apps/igt-gpu-tools: update USE flags for meson

x11-apps/igt-gpu-tools: update USE flags for meson

Initially the igt-gpu-tools meson build system had no optional
dependencies so all USE flags were forced on.

This commit restores the ability to disable optional dependencies and
restructures the USE flags from dependency-based (alsa, gsl, xrandr) to
feature-based (sound, overlay).

Closes: https://bugs.gentoo.org/670282
Closes: https://github.com/gentoo/gentoo/pull/11946
Signed-off-by: Denis Lisov <dennis.lissov@gmail.com>
Signed-off-by: Matt Turner <mattst88@gentoo.org>