marvell: a8k: set BL33 to /dev/null

TF-A build for Marvell a8k requires u-boot binary to be specified in
BL33 variable. As CI does not test and check compilation of u-boot, set
BL33 just to /dev/null like it is for SCP_BL2.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: If3bc38a0dcd9891a6bd5ae4ff17a879e43a0f0b8
7 files changed