pandaboard_defconfig: bump linux to 4.19.62 to fix build with gcc 8

pandaboard_defconfig: bump linux to 4.19.62 to fix build with gcc 8

The recent change to default to gcc 8 for the internal toolchain broke this
defconfig.  Fix it by bumping to the latest 4.19 kernel.

Fixes: https://gitlab.com/buildroot.org/buildroot/-/jobs/259853955
The kernel now uses ttySx for the omap serial ports, so adjust the getty
port to match.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>