staging: et131x: clear up use of TRUEPHY defines

There are a large number of TRUEPHY defines in the driver, all of which
are unused or unnecessary. Remove / replace these.

As this results in et1310_phy_access_mii_bit() only being used for
reading bits, also change it's name to et1310_phy_read_mii_bit().

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>