ar71xx: add dummy debugfs support for the ag71xx driver

target/linux/ar71xx/config-2.6.30

target/linux/ar71xx/config-2.6.31

target/linux/ar71xx/config-2.6.32

target/linux/ar71xx/files/drivers/net/ag71xx/Kconfig

target/linux/ar71xx/files/drivers/net/ag71xx/Makefile

target/linux/ar71xx/files/drivers/net/ag71xx/ag71xx.h

target/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_ar8216.c

...et/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_debugfs.c

...et/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_ethtool.c

target/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_main.c

target/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_mdio.c

target/linux/ar71xx/files/drivers/net/ag71xx/ag71xx_phy.c