disk: define HAVE_BLOCK_DEVICE in a common place

This set of ifdefs is used in a number of places. Move its definition
somewhere common so it doesn't have to be repeated.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Tom Rini <trini@ti.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>