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/device/tty/probe.go

@@ -2,10 +2,10 @@ package tty
 
 import "gopheros/device"
 
-// HWProbes returns a slice of device.ProbeFn that can be used by the hal
-// package to probe for TTY device hardware.
-func HWProbes() []device.ProbeFn {
-	return []device.ProbeFn{
-		probeForVT,
-	}
-}
+var (
+	// ProbeFuncs is a slice of device probe functions
+	// that is used by the hal package to probe for TTY
+	// hardware. Each driver should use an init() block
+	// to append its probe function to this list.
+	ProbeFuncs []device.ProbeFn
+)

src/gopheros/device/tty/vt.go

@@ -260,6 +260,8 @@ func (t *VT) DriverVersion() (uint16, uint16, uint16) {
 // DriverInit initializes this driver.
 func (t *VT) DriverInit() *kernel.Error { return nil }
 
-func probeForVT() device.Driver {
-	return NewVT(DefaultTabWidth, DefaultScrollback)
+func init() {
+	ProbeFuncs = append(ProbeFuncs, func() device.Driver {
+		return NewVT(DefaultTabWidth, DefaultScrollback)
+	})
 }