egl: return corresponding offset of EGLImage instead of 0.

egl: return corresponding offset of EGLImage instead of 0.

The offset should not always be 0. For example, if EGLImage is
created from a 2D texture with EGL_GL_TEXTURE_LEVEL=1, then the
offset should be the actual start of miplevel 1 in bo.

v2: Add version check of __DRIimageExtension implementation
(Suggested by Axel Davy).

v3: Don't add version check of __DRIimageExtension implementation.
Set the offset only when queryImage() succeeds. (Suggested by Emil
Velikov)

Signed-off-by: Chuanbo Weng <chuanbo.weng@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
[Emil Velikov: coding style fixes]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>