Allow depth peeling on AMD Radeon HD

Depth peeling works on newer(OpenGL > 3) AMD
Radeon HD devices. However, proxy texture memory
qureries with target PROXY_TEXTURE_RECTANGLE_ARB
does not work because of a driver bug. This patch
enables depth peeling for these devices but checks
MAX_TEXTURE_SIZE in place of the proxy query. Also,
the query need only be made once for each format
in preparation for the depth peels.

Change-Id: I96bfb839c0fbe2350b2efff75dd4e507c773e26a
Merge topic 'amd-radeon-hd-depth-peeling' into master

86debd03 Allow depth peeling on AMD Radeon HD