RDMA/hfi1: Use FIELD_GET() to extract Link Width

RDMA/hfi1: Use FIELD_GET() to extract Link Width

Use FIELD_GET() to extract PCIe Negotiated Link Width field instead of
custom masking and shifting, and remove extract_width() which only
wraps that FIELD_GET().

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230919125648.1920-2-ilpo.jarvinen@linux.intel.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dean Luick <dean.luick@cornelisnetworks.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>