configs/orangepi_zero_plus_defconfig: switch to mainline TF-A

Use the same TF-A as orangepi_zero_plus2 board.

Fixes: https://gitlab.com/buildroot.org/buildroot/-/jobs/2720001176



Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>