net: cpsw: Add support to drive gpios for ethernet to be functional

net: cpsw: Add support to drive gpios for ethernet to be functional

On DRA72 EVM, cpsw slaves may be muxed with other modules. This
selection is controlled by a pcf gpio line. Add support for cpsw driver
to acquire mode-gpios and select the appropriate slave using gpio APIs.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>