test: gen_perf: Add more test cases for IMX390 (4, 6 and 8 ch)

[ravi-rahul]

Signed-off-by: Abhay Chirania a-chirania@ti.com Signed-off-by: Rahul T R r-ravikumar@ti.com Co-authored-by: Rahul T R r-ravikumar@ti.com