[fast/warm-reboot] add cpufreq.default_governor=performance to BOOT_OPTIONS (#3435)

* [fast/warm-reboot] add cpufreq.default_governor=performance to BOOT_OPTIONS

Append this option to BOOT_OPTIONS variable.

How to verify it
Run fast-reboot or warm-reboot. Check:

admin@sonic:~$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
performance
After boot is finalized check that it is reset back to default:

admin@sonic:~$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
schedutil
---------

Signed-off-by: Stepan Blyschak <stepanb@nvidia.com>

Author: stepanblyschak

scripts/fast-reboot

@@ -422,6 +422,12 @@ function setup_reboot_variables()
         local fstype=$(blkid -o value -s TYPE ${sonic_dev})
         BOOT_OPTIONS="${BOOT_OPTIONS} ssd-upgrader-part=${sonic_dev},${fstype}"
     fi
+
+    if [[ "$sonic_asic_type" == "mellanox" ]]; then
+        # Set governor to performance to speed up boot process.
+        # The governor is reset back to kernel default in warmboot-finalizer script.
+        BOOT_OPTIONS="${BOOT_OPTIONS} cpufreq.default_governor=performance"
+    fi
 }
 
 function check_docker_exec()