phycore_am64x_a53_defconfig: Enable CONFIG_BOARD_LATE_INIT

Enable CONFIG_BOARD_LATE_INIT to use PHYTECs common board_late_init()
to set handy environment variables for u-boot.
Also, resync after savedefconfig.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>