plat/arm:juno: fix parallel build issue for romlib config

When building TF-A with USE_ROMLIB=1 and -j make options, the build fails with the following error:
make[1]: *** No rule to make target '/build/juno/debug/romlib/romlib.bin', needed by 'bl1_romlib.bin'.
This patch fixes that issue.

Signed-off-by: Zelalem <zelalem.aweke@arm.com>
Change-Id: I0cca416f3f50f400759164e0735c2d6b520ebf84
1 file changed