sys/targets: use a better DataOffset for linux/s390x
sys/targets: use a better DataOffset for linux/s390x

Use as data offset the address 0xfffff000 for s390x arch.
It is better for testing because it crosses the 4GB address space.

Signed-off-by: Alexander Egorenkov <91da4175525e9dfd14770d775671f3c95d603858@ibm.com>

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