e1000e: use default settings for Tx Inter Packet Gap timer

Use the default hardware values for TIPG except for 80003es2lan(*).  The
code that is removed in this patch is either unnecessarily writing the TIPG
register with the hardware default values for some devices (82571/2/3/4) or
writing the wrong value for others (ICH/PCH LOMs).  The only change in
functionality is setting the correct default TIPG for the latter devices.

(*) The correct value for 80003es2lan is already set properly in
e1000_init_hw_80003es2lan() and e1000_cfg_kmrn_{10_100|1000}_80003es2lan(),
and the unused flag FLAG_TIPG_MEDIUM_FOR_80003ESLAN is removed.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>