[XCelium] Enable coverage collection with XCelium
[XCelium] Enable coverage collection with XCelium

Includes a minor change in the simulator.yaml file to pass coverage
related flags to xrun.

Signed-off-by: Canberk Topal <e6b05429a51cc3258c31cb1f7836595b60921a29@lowrisc.org>

google/riscv-dv,google/riscv-dv,google/riscv-dv