sbsa-acs : Update arm_sbsa_testcase_checklist.md and create a test for S_L6SM_04, as it is effectively covered by BSA SMMU tests

[sunnywang-arm]

S_L6SM_04 is effectively covered by B_SMMU_03, B_SMMU_04, B_SMMU_05, B_SMMU_13, B_SMMU_14, and B_SMMU_23 tests

We may create a test for S_L6SM_04 to run B_SMMU_03, B_SMMU_04, B_SMMU_05, B_SMMU_13, B_SMMU_14, and B_SMMU_23 tests.