Fix the W5500 PHY configuration

[brianrho]

Not sure there's any activity still happening in this repo, so this is more for anyone else who runs into the same PHY configuration issue.

This commit fixes the following:

• Whenever the application specifies PHY_MODE_AUTONEGO in the wizphy_setphyconf argument, the function would unconditionally configure the PHY for "All Modes Capable". This is not quite in line with the datasheet, which permits 100BT+HDX to be paired with Auto-Negotiation.
• PHYCFGR_OPMDC_100FA seems to have been misnamed all this time -- it should've been called PHYCFGR_OPMDC_100HA since the Auto-negotiation is paired with 100BT-HDX, not 100BT-FDX.
• When reading the current PHY conf in wizphy_getphyconf, the above misnaming meant that the function would incorrectly return 100BT-FDX + Auto-nego, when the real conf is actually 100BT-HDX + Auto-Nego.
• Avoid unintentional PHY reset when setting the configuration -- this is done by masking all but the RST bit of the PHYCFGR, when assembling the bits for the requested configuration.