e1000e: Separate TGP board type from SPT

We have the same LAN controller on different PCHs. Separate TGP board
type from SPT which will allow for specific fixes to be applied for
TGP platforms.

Suggested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Tested-by: Mark Pearson <markpearson@lenovo.com>
Tested-by: Nechama Kraus <nechamax.kraus@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>