Xvfb/glamor inspired changes
Couple of small changes for the API and functionality, which correlate with the proposed Xvfb/glamor support.
The link is not obvious, so a short version is that now glamor_egl is xf86 agnostic (in order to be used by Xvfb), hence some trivial changes to this driver are needed.
Note: the commit lack a upstream sha reference and the XORG_VERSION_NUMERIC() used may need some polish depending on when that work lands.