thermal: provide an UAPI header file

include/linux/thermal.h contains definitions for the Thermal generic
netlink family, but none of the valuable information relevant to
user-space such as the Genl family name, multicast group, version or
command set and data types is exported to user-space.

Export all the relevant generic netlink information to user-space to
make this genl family usable by user-space, and while at it, export
THERMAL_NAME_LENGTH since it limits name length for thermal_hwmon
devices.

Kbuild and MAINTAINERS are also updated accordingly to reflect this new
file: include/uapi/linux/thermal.h.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 0ff630d..9c709f5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9295,6 +9295,7 @@
 S:	Supported
 F:	drivers/thermal/
 F:	include/linux/thermal.h
+F:	include/uapi/linux/thermal.h
 F:	include/linux/cpu_cooling.h
 F:	Documentation/devicetree/bindings/thermal/