Enable setting gridseed frequency through API
API modified to show hashrates in KHS
Add Frequency and Voltage to DEV

Conflicts:
	driver-gridseed.c
Add back MHS to make UI easier to handle
Reset the gridseed devices on shutdown, so they become idle
Actually call gridseed driver's thread_shutdown().

When shuting down hash_work() was never ending or breaking
its do-while loop therefore the mining thread was getting
killed off before the call to thread_shutdown(). This may
not be the correct solution (something else may be wrong),
but works for now.