opengles emulator: fix GL_EXT_packed_depth_stencil string

It used to be a GL_NV_packed_depth_stencil string extension, but
now it's GL_EXT_packed_depth_stencil and implemented by everyone. on
nVidia drivers both are exported.

Change-Id: I1b4af8a776f9957838d466b24fe73fa873ea85e4
6 files changed