gallium: interface cleanups, remove nblocksx/y from pipe_texture and more

gallium: interface cleanups, remove nblocksx/y from pipe_texture and more

This patch removes nblocksx, nblocksy arrays from pipe_texture (can be
recalculated if needed). Furthermore, pipe_format_block struct is gone
completely (again, contains just derived state).
nblocksx, nblocksy, block are also removed from pipe_transfer, together with
the format enum (can be obtained from the texture associated with the transfer).