oh/elink/sw/burst-test

Test burst writes

https://github.com/parallella/oh/issues/37

Remembered that we have a long forgotten mode in the epiphany chip elink (not impemented in the fpga elink) that creates bursts when you write doubles to the same address. (F**K!) So the writes were likely coming in as bursts. Looks like the mailbox works fine when you write in "int"s (I tested it on the board with consecutive) (see "mailbox_test" in elink/sw0)