drivers: ethernet: phy: microchip_t1s: fix C45 registers direct access

C45 direct registers access is only supported by the LAN865x internal PHY,
not by the LAN867x external PHY, even though the MAC supports it. Restrict
C45 direct register access to the LAN865x internal PHY. The LAN867x
external PHY supports C45 registers only via indirect access through C22
registers.

Signed-off-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>