RMX1921: Disable serial console notification

Google added a check for this prop in R, and if it's running
it will show a notification about it that it's impacting performance.
Why it's not disabled by default I don't know, so just force disable
it here.

Change-Id: Ia06ef15388e7e701ed526664e7748f133ad01ee2
Signed-off-by: kaderbava <ksbava7325@gmail.com>