drm/nouveau/therm: skip probing for devices not specified in thermal tables

Saves some time during driver load, as described by the relevant section[1]
of the DCB 4.x specification.

[1] https://nvidia.github.io/open-gpu-doc/DCB/DCB-4.x-Specification.html#_i2c_device_tableSigned-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/subdev/bios/extdev.h

@@ -26,4 +26,6 @@ nvbios_extdev_parse(struct nvkm_bios *, int, struct nvbios_extdev_func *);
 int
 nvbios_extdev_find(struct nvkm_bios *, enum nvbios_extdev_type,
 		   struct nvbios_extdev_func *);
+
+bool nvbios_extdev_skip_probe(struct nvkm_bios *);
 #endif

drivers/gpu/drm/nouveau/nvkm/subdev/bios/extdev.c

@@ -46,6 +46,19 @@ extdev_table(struct nvkm_bios *bios, u8 *ver, u8 *hdr, u8 *len, u8 *cnt)
 	return extdev + *hdr;
 }
 
+bool
+nvbios_extdev_skip_probe(struct nvkm_bios *bios)
+{
+	u8  ver, hdr, len, cnt;
+	u16 data = extdev_table(bios, &ver, &hdr, &len, &cnt);
+	if (data && ver == 0x40 && hdr >= 5) {
+		u8 flags = nvbios_rd08(bios, data - hdr + 4);
+		if (flags & 1)
+			return true;
+	}
+	return false;
+}
+
 static u16
 nvbios_extdev_entry(struct nvkm_bios *bios, int idx, u8 *ver, u8 *len)
 {

drivers/gpu/drm/nouveau/nvkm/subdev/therm/ic.c

@@ -116,6 +116,9 @@ nvkm_therm_ic_ctor(struct nvkm_therm *therm)
 			return;
 	}
 
+	if (nvbios_extdev_skip_probe(bios))
+		return;
+
 	/* The vbios doesn't provide the address of an exisiting monitoring
 	   device. Let's try our static list.
 	 */