usb: net: migrate USB Ethernet adapters to Kconfig

This migrates ASIX, ASIX88179, MCS7830, RTL8152 and SMSC95XX to Kconfig.
Update defconfigs.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/seaboard_defconfig b/configs/seaboard_defconfig
index 38760b5..ea4546b 100644
--- a/configs/seaboard_defconfig
+++ b/configs/seaboard_defconfig
@@ -38,6 +38,7 @@
 CONFIG_USB_KEYBOARD=y
 CONFIG_SYS_USB_EVENT_POLL=y
 CONFIG_USB_HOST_ETHER=y
+CONFIG_USB_ETHER_ASIX=y
 CONFIG_DM_VIDEO=y
 CONFIG_VIDEO_TEGRA20=y
 CONFIG_CONSOLE_SCROLL_LINES=10