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/T4240RDB_SDCARD_defconfig b/configs/T4240RDB_SDCARD_defconfig
index 4653052..1173f9f 100644
--- a/configs/T4240RDB_SDCARD_defconfig
+++ b/configs/T4240RDB_SDCARD_defconfig
@@ -52,6 +52,7 @@
 CONFIG_SF_DEFAULT_SPEED=10000000
 CONFIG_SPI_FLASH_SST=y
 CONFIG_PHYLIB=y
+CONFIG_PHY_CORTINA=y
 CONFIG_PHY_GIGE=y
 CONFIG_E1000=y
 CONFIG_FMAN_ENET=y