egl/x11: Handle depth 30 drawables for EGL_KHR_image_pixmap.

egl/x11: Handle depth 30 drawables for EGL_KHR_image_pixmap.

Enables eglCreateImageKHR() with target set to
EGL_NATIVE_PIXMAP_KHR to handle color depth 30
X11 drawables.

Note that in theory the drawable depth 32 case in the
current implementation is ambiguous: A depth 32 drawable
could be of format ARGB8888 or ARGB2101010, therefore an
assignment of __DRI_IMAGE_FORMAT_ARGB8888 for a pixmap of
ARGB2101010 format would be wrong. In practice however, the
X-Server (as of v1.19) does not provide any depth 32 visuals
for ARGB2101010 EGL/GLX configs. Those are associated with
depth 30 visuals without an alpha channel instead. Therefore
the switch-case depth 32 branch is only executed for ARGB8888
pixmaps and we get away with this.

Tested with KDE Plasma 5 under X11, DRI2 and DRI3/Present,
selecting EGL + OpenGL compositing and different fbconfigs
with/without 2 bit alpha channel. glxinfo confirms use of
depth 30 visuals for ARGB2101010 only.

Suggested-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>