Understanding this code is getting out of control without any
notes. Give the firmware_class driver a much needed documentation love,
and while at it convert it to the new sphinx documentation format.

v2: typos and small fixes
Signed-off-by: NLuis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>