MFC: r225014

MFC: r225014

r221812 (MFC'ed to stable/8 in r222159) reveals that at least some Broadcom
PHYs default to being not only isolated but also powered down after a reset
and while they just work fine [sic] when both is the case they don't if they
are only deisolate but still powered down. So in order to put PHYs in an
overall normal operation mode for the common case, ensure in mii_phy_reset()
that they are not powered down after a reset. Unfortunately, this only helps
in case of BCM5421, while BCM5709S apparently only work when they remain
isolated and powered down after a reset. So don't call mii_phy_reset() in
brgphy_reset() and implement the reset locally leaving the problematic bits
alone. Effectively this bypasses r221812 for brgphy(4).
Thanks to Justin Hibbits for doing a binary search in order to identify
the problematic commit.

PR:		157405, 158156
Reviewed by:	yongari (mii_phy_reset() part)

git-svn-id: svn://svn.freebsd.org/base/stable/8@225116 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f