core: Added attach_surface() to the renderer interface.

core: Added attach_surface() to the renderer interface.

In order to draw a view, the surface of the view should be attached to the
renderer first. For pixman renderer, we need a pixman_image_t for the given
surface's current buffer. For gl renderer, we need a texture.

Size of a buffer is unknown until it is attached to a renderer for some types
of buffers, for example, size of an EGL buffer can be queried via
eglQueryWaylandBufferWL() so the core should attach the buffer to a renderer
in order to get its size.

Normaly, only shm buffers can be attached to pixman renderers. But there're
platforms that can map DMABUFs into CPU address so that pixman renderer can
serve those types of buffers.

Change-Id: I4c07b48d1879a3c2d2d4c26db67b41019071458b