sdl2: new package

sdl2: new package

[Romain:
  - Wrap Config.in help text at 72 columns.
  - Move sdl2 package after sdl modules in Config.in. (Arnout)
  - Explicitly disable dbus and wayland.
  - Remove double underscore (SDL2__*).
  - Unify autotools options to use --enable/--disable.
  - Use x-includes and x-libraries to avoid path poisoning.
  - Remove xlib_libXrender, xproto_inputproto and xproto_scrnsaverproto
    dependencies since the build system doesn't depend on them.
  - Add Xlib_libXi, xlib_libScrnSaver and xlib_libXxf86vm dependencies.
  - Handle autotools options (--enable/--disable) for each X11
    dependencies.]

[Thomas:
  - Minor tweaks to Config.in
  - Addition of hash file.
  - Addition of SDL2_CONFIG_SCRIPTS, as suggested by Vincent Stehlé.]

Signed-off-by: Guillaume GARDET <guillaume.gardet@oliseo.fr>
Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Cc: Yann E. Morin <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>