configs: am65x_evm_a53: add SPL_LOAD_FIT_APPLY_OVERLAY

We want SPL to apply DTB overlays (e.g. ICSSG2 overlay) so enable
SPL_LOAD_FIT_APPLY_OVERLAY.

Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Acked-by: Ravi Gunasekaran <r-gunasekaran@ti.com>