[pddf]: Adding and enabling S3IP support in PDDF (#15073)

Why I did it
The S3IP (Simplified Switch System INtegration Program) sysfs specification defines a unified interface to access peripheral hardware on devices from different vendors, making it easier for SONiC to support different devices and platforms.

PDDF is a framework to simplify the driver and SONiC platform APIs development for new platforms. This effort is first step in combining the two frameworks.

This specific PR adds support for pddf-s3ip-init.service and enables it in PDDF.

platform/pddf/i2c/service/pddf-s3ip-init.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=S3IP sysfs creation in PDDF based platforms
+After=pddf-platform-init.service
+DefaultDependencies=no
+
+[Service]
+Type=oneshot
+ExecStartPre=-/usr/local/bin/pre_pddf_s3ip.sh
+ExecStart=/usr/local/bin/pddf_s3ip.py create
+ExecStop=/usr/local/bin/pddf_s3ip.py clean
+RemainAfterExit=yes
+
+[Install]
+WantedBy=multi-user.target

platform/pddf/i2c/utils/pddf_util.py

@@ -455,6 +455,11 @@ def do_install():
     if status:
         return status
 
+    # Check if S3IP support is enabled, if yes, start the service in no block mode
+    if 'enable_s3ip' in pddf_obj.data['PLATFORM'].keys() and pddf_obj.data['PLATFORM']['enable_s3ip'] == 'yes':
+        log_os_system('systemctl enable pddf-s3ip-init.service', 1)
+        log_os_system('systemctl start --no-block pddf-s3ip-init.service', 1)
+
     return
     
 def do_uninstall():