Add SDIO support.

Add a CAM-Newbus SDIO support module. This works provides a newbus
infrastructure for device drivers wanting to use SDIO. On the lower end
while it is connected by newbus to SDHCI, it talks CAM using the MMCCAM
framework to get to it.

This also duplicates the usbdevs framework to equally create sdiodev
header files with #defines for "vendors" and "products".

Submitted by: kibab (initial work, see https://reviews.freebsd.org/D12467)
Reviewed by: kibab, imp (comments on earlier version)
MFC after: 6 weeks
Relnotes: yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D19749