Move PHYLIB to Kconfig

Signed-off-by: Alexandru Gagniuc <alex.g@adaptrum.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/riotboard_defconfig b/configs/riotboard_defconfig
index fb9e9b0..04b2653 100644
--- a/configs/riotboard_defconfig
+++ b/configs/riotboard_defconfig
@@ -21,6 +21,7 @@
 CONFIG_DM=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_SST=y
+CONFIG_PHYLIB=y
 CONFIG_DM_THERMAL=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y