tinytile: support flashing

Now both flashing over DFU and JTAG are supported, however JTAG needs a
special connection, so DFU is the current out of the box supported
method for flashing.

Jira: ZEP-1785
Change-Id: I47ffce3b332b99ef6c6afdce2214709a4fa5b946
Signed-off-by: Anas Nashif <anas.nashif@intel.com>