drivers: net: cpsw: fix get mdio base and gmii_sel reg from DT

drivers: net: cpsw: fix get mdio base and gmii_sel reg from DT

Since dra7x platforms address bus is define as 64 bits to support
LAPE, fdtdec_get_addr() returns a invalid address for mdio based
and gmii_sel register address. Fixing this by using
fdtdec_get_addr_size_auto_noparent() which will derive address
cell and size cell from its parent.

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