wil6210: add 'info' debugfs entry

Use 'info' debugfs entry for misc. assorted information.
Start with indication whether platform is AC-powered;
will use it later for power related decisions

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>