ice: E825C PHY register cleanup

ice: E825C PHY register cleanup

Minor PTP register refactor, including logical grouping E825C 1-step
timestamping registers. Remove unused register definitions
(PHY_REG_GPCS_BITSLIP, PHY_REG_REVISION).
Also, apply preferred GENMASK macro (instead of ICE_M) for register
fields definition affected by this patch.

Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Signed-off-by: Grzegorz Nitka <grzegorz.nitka@intel.com>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20250310174502.3708121-5-anthony.l.nguyen@intel.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>