arm: xea: spl: Add GPIO0_0 setup on spl_board_init

Explicitly configure GPIO0_0 in SPL, which controlls 3V3 voltage
on the XEA board (it also supplies TIVAs).

This code would enable TIVAs power supply early (also when board
uses the falcon boot).

Signed-off-by: Lukasz Majewski <lukma@denx.de>