ARM: dts: da850-evm: add serial and ethernet aliases

Add aliases for serial and ethernet nodes. Serial
aliases help keep order of tty nodes fixed and
ethernet alias is used by bootloader to setup mac
address correctly.

Reported-by: Adam Ford <aford173@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Fixes: dd7deaf2

 ("ARM: davinci: da850: add DT node for ethernet")
Signed-off-by: Sekhar Nori <nsekhar@ti.com>