odroid-mali: add support for x11 egl implementation

odroid-mali: add support for x11 egl implementation

Allow installation of the x11 egl support required for the X11 ddx
driver. The BR2_PACKAGE_ODROID_MALI_X11 hidden option will be selected
by the X11 DDX driver.

Signed-off-by: Dagg Stompler <daggs@gmx.com>
[Thomas:
 - select BR2_PACKAGE_LIBDRM,
   BR2_PACKAGE_XLIB_{LIBX11,LIBXFIXES,LIBXEXT,LIBXDAMAGE} from
   BR2_PACKAGE_ODROID_MALI_X11 in order to avoid numerous "if" in
   Config.in
 - Use a single assignment to ODROID_MALI_DEPENDENCIES to add the
   dependencies for libdrm and the X11 libraries.
 - Introduce ODROID_MALI_HEADERS_SUBDIR and ODROID_MALI_LIBS_SUBDIR to
   clarify the location of the headers and libraries for the selected
   architecture/display backend in the Mali tree.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>