i965: Lift restriction in external textures for EGLImage support

i965: Lift restriction in external textures for EGLImage support

Fixes Skqp's unitTest_EGLImageTest test.

For Intel platforms, we support external textures only for EGLImages
created with EGL_EXT_image_dma_buf_import. This restriction seems to
be Intel specific and not present for other platforms.

While running SKQP test - unitTest_EGLImageTest, GL_INVALID is sent
to the test because of this restriction.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105301
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Chad Versace <chadversary@chromium.org>