The passthrough ioctl has a userland ABI header, but nothing installed
it. A program that wanted to use the ioctl had to copy the headers out
of the source tree by hand.

Install ufshci.h and ufshci_ioctl.h under /usr/include/dev/ufshci, the
way nvme installs nvme.h. The ioctl header pulls in ufshci.h, so both
go. Add the directory to the include mtree so installworld creates it.

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