Add a workaround needed to fix a bug of Arasan Host Controller where it may
lose the contents of consecutive writes (that happens within two SD card
clock cycles).

This fixes the causes of instability during the SD card detection and
identification on Raspberry Pi (which happens at 400 kHz and so was much
more vulnerable to this issue).

Remove the previous workaround which clearly can't provide the same effect.

MFC after:	1 week
Relnotes:	yes


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273264 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f