- Clear the PCN_MISC_ASEL bit so the media port can be actually set

- Clear the PCN_MISC_ASEL bit so the media port can be actually set
  via the PCN_CSR_MODE register. Along with sys/dev/mii/nsphy.c 1.26
  this fixes the case of certain Am79c971-based HP cards and on-board
  ones in IBM machines reporting link but not actually passing any
  traffic. [1]
- Add support for the internal 10baseT PHY, which actually is used on
  at least said HP cards (together with an external DP83840A in a
  multiple PHYs configuration). With cards that don't make use of this
  internal PHY it'll also show up in FreeBSD but not cause any harm.
  This is still missing support for multiple PHYs configuration using
  the internal 100baseTX and/or HomePNA PHYs together with external
  PHYs or multiple external PHYs though.
- In pcn_ifmedia_upd() call pcn_reset() as otherwise the Am79C971 of
  at least said HP cards can wedge when switching from the internal
  10baseT PHY to the external PHY. This means that we need to also
  initialize and possibly start the chip again in pcn_ifmedia_upd(),
  which isn't that bad though as for setting the media port the chip
  has to be powered down or stopped anyway and unlike documented
  doesn't take effect until the next initialization.

PR:		27995, 25959, 72966 (likely) [1]
MFC after:	2 weeks