SDK: add missing GLES3 headers
In Dunfell the poky Mesa recipe always explicitely includes the GLES3-headers when building the GLES2-Dev-Target, (even with a comment "Add dependency so that GLES3 headers don't need to be added manually"). NXP's Vivante driver recipes do the same.
For some reason this has been removed in the Kirkstone poky Mesa recipe, resulting in the GLES3-headers missing in the SDK and thus causing Qt-apps to fail compilation, because some Qt-headers expect the GLES3 headers.
This patch adds the explicit includes of the GLES3-headers (this time in our own layer, though).
Edited by Marc-Oliver Westerburg