ARM: DRA7xx: add support for reading cpsw 2nd mac from efuse

Adding support for reading cpsw 2nd mac address from efuse and pass it
to kernel via dtb which will be used in dual emac mode of cpsw.
Also correct the bit masking of mac id read from the efuse.

Acked-by: Tom Rini <trini@ti.com>
Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>