Accelerate gldownload with directviv

1.Propose a physical buffer pool to upstream in gldownload
2.Bind the physical buffer with texture via dirctviv
3.In gldownload, wrap the physical buffer to gstbuffer, pass to
  downstream plugins.
4.Add some configure check for g2d and phymem

From GST-1.14, add GST_GL_API ahead api to export symbol
add include "gstglfuncs.h" when need call gl api

Upstream-Status: Inappropriate [i.MX specific]
6 files changed