Makefile: at91bootstrap: at91-sama5d4_xplained: use uboot secure.
Makefile: at91bootstrap: at91-sama5d4_xplained: use uboot secure.

Because it has no uboot (only) defconfig file.

Signed-off-by: Gaël PORTAY <1666f60cfa201a60b0ea694168a0b6932673170a@gmail.com>

gazoo74/at91nandflash