core: Enable DM by default

There are no longer any platforms which do not enable DM, move this to a
def_bool y and remove the check in the Makefile.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed