Limit reload BCM SDK kmods on syncd start to PikeZ platform (#12971)

Why I did it
Limiting #12804 changes to PikeZ platform only (Arista-720DT-48S). Note that this is a short term workaround for this platform until SDK investigation on SDK init failure on docker syncd restart due to DMA issues is resolved.

How I did it
Retrieve platform name from /host/machine.conf and only reload SDK kmods on Arista-720DT-48S platform.

Signed-off-by: Michael Li <michael.li@broadcom.com>

files/scripts/syncd.sh

@@ -30,6 +30,15 @@ function startplatform() {
 
     if [[ x"$sonic_asic_platform" == x"broadcom" ]]; then
         if [[ x"$WARM_BOOT" != x"true" ]]; then
+            . /host/machine.conf
+            if [ -n "$aboot_platform" ]; then
+                platform=$aboot_platform
+            elif [ -n "$onie_platform" ]; then
+                platform=$onie_platform
+            else 
+                platform="unknown"
+            fi
+            if [[ x"$platform" == x"x86_64-arista_720dt_48s" ]]; then
                 is_bcm0=$(ls /sys/class/net | grep bcm0)
                 if [[ "$is_bcm0" == "bcm0" ]]; then
                     debug "stop SDK opennsl-modules ..."
@@ -40,6 +49,7 @@ function startplatform() {
                 fi
             fi
         fi
+    fi
 
     if [[ x"$sonic_asic_platform" == x"barefoot" ]]; then
         is_usb0=$(ls /sys/class/net | grep usb0)