configs/snps_arc*_defconfig: update linux version

With this commit we update for ARC boards Linux kernel
version to 4.19.31 and Linux headers version to 4.19.

Signed-off-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: arc-buildroot@synopsys.com
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>