daemon/devices: Turn RegisterGPUDeviceDrivers into func

Change GPU device driver registration from init-time function assignment
to direct function exports.

This removes the init() function and global function variable pattern in
favor of a more explicit approach.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

daemon/devices.go

@@ -10,13 +10,10 @@ import (
 	"github.com/moby/moby/v2/daemon/config"
 	"github.com/moby/moby/v2/daemon/internal/capabilities"
 	"github.com/opencontainers/runtime-spec/specs-go"
-	"tags.cncf.io/container-device-interface/pkg/cdi"
 )
 
 var deviceDrivers = map[string]*deviceDriver{}
 
-var RegisterGPUDeviceDrivers = func(_ *cdi.Cache) {}
-
 type deviceListing struct {
 	Devices  []system.DeviceInfo
 	Warnings []string

daemon/devices_linux.go

@@ -2,14 +2,10 @@ package daemon
 
 import "tags.cncf.io/container-device-interface/pkg/cdi"
 
-func init() {
-	RegisterGPUDeviceDrivers = registerGPUDeviceDrivers
-}
-
-// registerGPUDeviceDrivers registers GPU device drivers.
+// RegisterGPUDeviceDrivers registers GPU device drivers.
 // If the cdiCache is provided, it is used to detect presence of CDI specs for AMD GPUs.
 // For NVIDIA GPUs, presence of CDI specs is detected by checking for the nvidia-cdi-hook binary.
-func registerGPUDeviceDrivers(cdiCache *cdi.Cache) {
+func RegisterGPUDeviceDrivers(cdiCache *cdi.Cache) {
 	// Register NVIDIA device drivers.
 	if nvidiaDrivers := getNVIDIADeviceDrivers(); len(nvidiaDrivers) > 0 {
 		for name, driver := range nvidiaDrivers {

daemon/devices_nonlinux.go

@@ -0,0 +1,8 @@
+//go:build !linux
+
+package daemon
+
+import "tags.cncf.io/container-device-interface/pkg/cdi"
+
+// RegisterGPUDeviceDrivers is a no-op on non-Linux platforms.
+func RegisterGPUDeviceDrivers(_ *cdi.Cache) {}