libertas: add sd8686 reset_card support

At http://dev.laptop.org/ticket/10748 we are seeing a case of the
libertas firmware randomly stopping responding to commands after
resume. Careful monitoring of communications indicates a firmware or
hardware bug, which has been reported to Marvell.

Work around this issue by adding a reset_card method; this is
automatically called when command timeouts are detected and provides an
instant recovery to this situation.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>