x86_pkg_temp_thermal: Fix the thermal zone type

The thermal zone type should not include an instance number. Otherwise
each zone is considered a different type and the thermal-to-hwmon
bridge fails to group them all in a single hwmon device.

I also changed the type to "x86_pkg_temp", because "pkg" was too
generic, and other thermal drivers use an underscore, not a dash, as
a separator. Or maybe "cpu_pkg_temp" would be better?

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>