r8169: merge firmware information into the chipset description data.

- RTL_GIGA_MAC_NONE is a fake index so put it at the end of the
  enumeration and shift everybody.
- RTL_GIGA_MAC_VER_17 / RTL_GIGA_MAC_VER_16 ordering fixed. Though
  not wrong it was confusing enough to wonder if things were right.

Renaming rtl_chip_info was not strictly necessary. It allows to
check the patch for the correct use of the indexes though.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Realtek linux nic maintainers <nic_swsd@realtek.com>