e1000e: Use PCI_EXP_LNKSTA_NLW & FIELD_GET() instead of custom defines/code

e1000e has own copy of PCI Negotiated Link Width field defines. Use the
ones from include/uapi/linux/pci_regs.h instead of the custom ones and
remove the custom ones and convert to FIELD_GET().

Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>