sky2: use PCI VPD API in eeprom ethtool ops

Recently pci_read/write_vpd_any() have been added to the PCI VPD API.
These functions allow to access VPD address space outside the
auto-detected VPD, and they can be used to significantly simplify the
eeprom ethtool ops.

Tested with a 88E8070 card with 1KB EEPROM.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>