sdhci.4: Improve HARDWARE for HW Relnotes + SPDX

MFC after: 1 hr
Discussed with: ivy, olce
Co-authored-by: ziaee (typed up imps suggestion, tagged spdx)
Differential Revision: https://reviews.freebsd.org/D52860

(cherry picked from commit bc433a0b7b046b0412777e0f3cc8f18a233af8ff)