Previous patch to support nosys.specs accidentally broke validation specs because...

Previous patch to support nosys.specs accidentally broke validation specs because ARM_RDI_MONITOR was never passed to the build rule for crt0.

This fixed the compile for nosys and validation specs
but nosys won't run because of existing limitations to
aarch64's syscalls.c, it requires semihosting to get
commandline arguments and heap info without having a
fallback method as ARM does.

Signed-off-by: Tamar Christina <tamar.christina@arm.com>