net: phy: add registers to support 1000BASE-T1

Add registers and definitions to support 1000BASE-T1. This includes the
PCS Control and Status registers (3.2304 and 3.2305) as well as some
missing bits on the PMA/PMD extended ability register (1.18) and PMA/PMD
CTRL (1.2100) register.

Signed-off-by: Stefan Eichenberger <eichest@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>