Makefile: Trigger a warning for legcay spi drivers

We have a warning text for non dm converted spi drivers, but the plan is
to mark all these respective drivers with CONFIG_DEPRECATED.

So, trigger a warning saying that these driver configurations and
associated code will remove in v2019.07 (earlier plan is to remove it
from v2019.04)

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
1 file changed