aw_mmc: Reset card

On H616 (and I think H6, but this isn't verified) we need to reset the
card to have a functioning device.

With this commit all my pending patches for H616 are in tree. We run
well on my test device (Orange Pi Zero3), however there is an
uninvestigated issue with ethernet and graphics are an open question.

Reviewed by: manu, adrian
MFC After: 1 week
Relnotes: yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55097