si clock for the lpc
firmware: remove 5mhz option
tools: fix hackrf_si5351c to print ms6 and 7

6 and 7 are integer only. Also fixes printing of the output divider
value.
lib: fix mingw
tools: add gain control
disable si clock to lpc

leaving it on but unused causes major spurs to appear all over the
place..
Merge pull request #66 from Hoernchen/siclock

si clock for the lpc