Revised createTextureFromBuffer

The context is not passed anymore to texture() and similar functions since
they have to use the current context anyhow.

createTextureFromBuffer() becomes bindTextureToBuffer() which is called
with the texture bound. The integration can also provide its own texture in
case the one created and managed by the surfacebuffer is not suitable.

Change-Id: I1bfc4fe35c0e3db6081b47c551f20f4bca9aa04e
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>