ice: Remove and replace ice speed defines with ethtool.h versions

The driver is currently using ICE_LINK_SPEED_* defines that mirror what
ethtool.h defines, with one exception ICE_LINK_SPEED_UNKNOWN.

This issue is fixed by the following changes:

1. replace ICE_LINK_SPEED_UNKNOWN with 0 because SPEED_UNKNOWN in
   ethtool.h is "-1" and that doesn't match the driver's expected behavior
2. transform ICE_LINK_SPEED_*MBPS to SPEED_* using static tables and
   fls()-1 to convert from BIT() to an index in a table.

Suggested-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Co-developed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>