gallium: add PIPE_RESOURCE_FLAG_TEXTURING_MORE_LIKELY

gallium: add PIPE_RESOURCE_FLAG_TEXTURING_MORE_LIKELY

For performance tuning in drivers. It filters out window system
framebuffers and OpenGL renderbuffers.

radeonsi will use this to guess whether a depth buffer will be read
by a shader. There is no guarantee about what will actually happen.

This is a departure from PIPE_BIND flags which are defined to be strict
but they are useless in practice.

Acked-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>