[chip, dv] Change m_tl_agent_cfg.max_outstanding_req to 8
[chip, dv] Change m_tl_agent_cfg.max_outstanding_req to 8

This TL agent is used in stub_cpu mode and connected with ibex data port.
It can have up to 8 outstanding items due to the async fifos in the xbar.
However, the actual ibex data port can only support 1 outstanding item.

Signed-off-by: Weicai Yang <4fa8c7762ee4da95e3dee7dae2c3263ea16637f9@google.com>

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