Each driver should manually register a probe function for use by hal

This commit removes the HWProbes() function from the console and tty
packages and replaces it with a global ProbeFuncs slice which is fetched
by the hal package when the hardware autodetection code runs.

Each driver should provide an init() function that appends a probe function
to the global ProbeFuncs slice.

This approach allows us to support conditional compilation of drivers in
the future (e.g. using build tags)

src/gopheros/kernel/hal/hal.go

@@ -23,12 +23,12 @@ func ActiveTTY() tty.Device {
 // DetectHardware probes for hardware devices and initializes the appropriate
 // drivers.
 func DetectHardware() {
-	consoles := probe(console.HWProbes())
+	consoles := probe(console.ProbeFuncs)
 	if len(consoles) != 0 {
 		devices.activeConsole = consoles[0].(console.Device)
 	}
 
-	ttys := probe(tty.HWProbes())
+	ttys := probe(tty.ProbeFuncs)
 	if len(ttys) != 0 {
 		devices.activeTTY = ttys[0].(tty.Device)
 		devices.activeTTY.AttachTo(devices.activeConsole)