Use tmpfs for /var/log for Arista 7260 (sonic-net#13587)

This is to reduce writes to disk, which then can use the SSD to get worn
out faster.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

files/Aboot/boot0.j2

@@ -502,6 +502,7 @@ write_platform_specific_cmdline() {
     if [ "$sid" = "Gardena" ] || [ "$sid" = "GardenaE" ]; then
         aboot_machine=arista_7260cx3_64
         flash_size=28000
+        cmdline_add logs_inram=on
     fi
     if [ "$sid" = "Alhambra" ]; then
         aboot_machine=arista_7170_64c