[portconfig]: Remove try block for db config initialization (#10581)

Why I did it
Provide fix for comment: https://github.com/Azure/sonic-buildimage/pull/10475/files#r847753187;
How I did it
Try exception is not required in this scenario, so remove and modify to initial db config according to single or multi-asic platforms.
How to verify it
Verified on multi-asic device.

src/sonic-config-engine/portconfig.py

@@ -72,12 +72,7 @@ def db_connect_configdb(namespace=None):
     """
     Connect to configdb
     """
-    try:
-        if namespace is not None:
-            swsscommon.SonicDBConfig.load_sonic_global_db_config(namespace=namespace)
-        config_db = swsscommon.ConfigDBConnector(use_unix_socket_path=True, namespace=namespace)
-    except Exception as e:
-        return None
+    config_db = swsscommon.ConfigDBConnector(use_unix_socket_path=True, namespace=namespace)
     if config_db is None:
         return None
     try:

src/sonic-config-engine/sonic-cfggen

@@ -32,7 +32,7 @@ from functools import partial
 from minigraph import minigraph_encoder, parse_xml, parse_device_desc_xml, parse_asic_sub_role, parse_asic_switch_type
 from portconfig import get_port_config, get_breakout_mode
 from redis_bcc import RedisBytecodeCache
-from sonic_py_common.multi_asic import get_asic_id_from_name, get_asic_device_id
+from sonic_py_common.multi_asic import get_asic_id_from_name, get_asic_device_id, is_multi_asic
 from sonic_py_common import device_info
 from swsscommon.swsscommon import SonicV2Connector, ConfigDBConnector, SonicDBConfig, ConfigDBPipeConnector
 
@@ -309,6 +309,12 @@ def main():
                                 'localhost': {'namespace_id': namespace_id}
                              }
                           })
+    # load db config
+    if not SonicDBConfig.isInit():
+        if is_multi_asic():
+            SonicDBConfig.load_sonic_global_db_config(namespace=asic_name)
+        else:
+            SonicDBConfig.load_sonic_db_config()
     if hwsku is not None:
         hardware_data = {'DEVICE_METADATA': {'localhost': {
             'hwsku': hwsku