With the current implementation of GPIO hogging and with
gpio-pcf857x is built as module, ethernet doesn't work on boot
and doesn't throw any error/warning to user. Ethernet becomes
operational when inserting gpio-pcf857x module, even this time
there is no error/warning logs to user that ethernet is
operational.

When using with NFS rootfs and gpio-pcf857x as module, board
doesn't boot as it doesn't get any ip address and doesn't throw
any error/warning. To over come this, now cpsw driver tries to
get mode-gpios. When gpio-pcf857x is built as module it will
throw error, so that user can decide either to built in
gpio-pcf857x to continue with nfs boot or choose alternate rootfs
filesystem like sd/ramdisk.

When using mmc/ramdisk as root fs, cpsw will probe defer and
re-probes again when gpio-pcf857x module is inserted and ethernet
becomes operational.
Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>