icorem6: Make SPL to pick suitable fdt

SPL FIT is able to pick the suitable fdt file for u-boot,
so add that function through board_fit_config_name_match.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>