HID: expose country code in sysfs

This commit exposes in sysfs the HID country code that is stored in the country
member of hid_device structure. It identifies the country code of localized
hardware.

For example some keyboards use it to exhibit the language of the key layout. It
helps the upper layer to identify the localized hardware and setup the correct
language to use.

For USB HID devices the country code comes for the HID descriptor and for
Bluetooth HID devices it is the HIDCountryCode attribute from the SDP database.

Signed-off-by: Olivier Gay <ogay@logitech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>