Convert CONFIG_PHY_CORTINA to Kconfig

This converts the following to Kconfig:
   CONFIG_PHY_CORTINA

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/T2080RDB_NAND_defconfig b/configs/T2080RDB_NAND_defconfig
index c0ce181..bed4fed 100644
--- a/configs/T2080RDB_NAND_defconfig
+++ b/configs/T2080RDB_NAND_defconfig
@@ -62,6 +62,7 @@
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_AQUANTIA=y
+CONFIG_PHY_CORTINA=y
 CONFIG_E1000=y
 CONFIG_FMAN_ENET=y
 CONFIG_MII=y