As part of tier0 unification across the rhel-pt-gcc components
(RHEL-113756), redefine tier0 testing.
Replace the four existing tests (outdated and disconnected copies
from the public part of tier1) with a pointer to the public part
tier1 directly and use it whole, albeit on x86_64-only (this
limitation is OSCI-imposed).
For awareness, RHEL builds get full tier1 (including non-public
tests and all the architectures) in a later phase of gating
(BaseOS CI). This commit doesn't affect that in any way; we are
just changing a small bit of functional testing sooner in the
pipeline.
