platform/x86: thinkpad_acpi: sysfs interface to get wwan antenna type

platform/x86: thinkpad_acpi: sysfs interface to get wwan antenna type

On some newer Thinkpads we need to set SAR value based on antenna type.
This patch provides a sysfs interface that userspace can use to get
antenna type and set corresponding SAR value, as is required for FCC
certification.

Reviewed-by: Mark Pearson <markpearson@lenovo.com>
Signed-off-by: Nitin Joshi <njoshi1@lenovo.com>
Link: https://lore.kernel.org/r/20210317024636.356175-1-njoshi1@lenovo.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>