protocol: Add content-protection protocol

protocol: Add content-protection protocol

This protocol allows a client to ask the compositor to only allow it to
be displayed on a "secure" output. This initial version of the protocol
supports HDCP.

This is loosely based on the chromium secure-output protocol [1].

This protocol is mostly useful for closed system, where the client can
trust the compositor, such as set-top boxes. This is not a way to
implement any kind of Digital Rights Management on desktops. The
compositor would be free to lie to the client, anyway.

Signed-off-by: Scott Anderson <scott.anderson@collabora.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
[1]
https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/secure-output/secure-output-unstable-v1.xml