Skip RDMA tests on specific hwsku based on support (sonic-net#8343)

### Description of PR
Summary:
There is a dependency between E2E test improvements PR: sonic-net#8341 and sonic-utilities GCU RDMA feature PR: sonic-net/sonic-utilities#2791

This PR skips the RDMA tests that will fail when the platform GCU RDMA feature PR is merged. After the GCU RDMA feature PR is merged and backported to the appropriate branch, we will revert this PR to stop skipping the E2E tests, and merge the E2E test improvements PR so that the tests will pass once the feature changes take effect.

tests/common/plugins/conditional_mark/tests_mark_conditions.yaml

@@ -448,6 +448,12 @@ generic_config_updater:
  conditions:
  - "'t2' in topo_name"
 
+generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates:
+ skip:
+ reason: "This test is not run on this asic type currently"
+ conditions:
+ - "asic_type in ['cisco-8000']"
+
 generic_config_updater/test_eth_interface.py::test_replace_fec:
  skip:
  reason: 'replace_fec ethernet test is not supported on virtual switch'
@@ -475,9 +481,16 @@ generic_config_updater/test_eth_interface.py::test_update_valid_invalid_index[33
 
 generic_config_updater/test_incremental_qos.py::test_incremental_qos_config_updates:
  skip:
- reason: "This test was not run on this hwsku type currently"
+ reason: "This test is not run on this hwsku/asic type currently"
  conditions:
  - "not any(i in hwsku for i in ['2700', 'Arista-7170-64C', 'montara', 'newport'])"
+ - "asic_type in ['broadcom', 'cisco-8000']"
+
+generic_config_updater/test_mmu_dynamic_threshold_config_update.py::test_dynamic_th_config_updates:
+ skip:
+ reason: "This test is not run on this asic type currently"
+ conditions:
+ - "asic_type in ['broadcom', 'cisco-8000']"
 
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