EGL: Add support for weston

EGL: Add support for weston

Add support for wayland & drm platforms which are used by weston.
Select EGL platform for weston by setting environment variable:
    export EGL_PLATFORM=wayland

Modifications to mesa.spec:
    Add platforms wayland and drm which is needed by weston
    Enable gbm and pack it into RPM package
Modifications to egl_dri2.h
    Since tizen, drm and wayland are all supported now, remove
    the duplicate definition of "color_buffers" and "back" for
    tizen to avoid from building error.

Merged commit:
commit 7c8922c1ead5875fda90106793c2fcfab2feb9f3
Author: Xiaowei Guan <xiaowei.guan@samsung.com>
    - fix weston build error and app launch error

commit 6e7ce80fc524b78980d702549cf5bbc3a641e6ae
Author: Xiaowei Guan <xiaowei.guan@samsung.com>
    - add wayland-egl code for platform_wayland

commit 5cd0256faa43e376dcd5b5f2c2edd2515aff9c04
Author: Zhaowei Yuan <zhaowei.yuan@samsung.com>
    - EGL: Add support for weston

Change-Id: I58272083b7d110d55800d8b9ad7e7c4f0a6f6077
Signed-off-by: Zhaowei Yuan <zhaowei.yuan@samsung.com>