phy: renesas: use SPDX identifier for Renesas drivers

Use SPDX identifier for Renesas drivers.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>