configs/pc_x86_64_{efi, bios}_defconfig: update kernel to 4.19.204

gcc 10.x is now used by default but the kernel 4.18.10 used by
pc_x86_64_{efi,bios}_defconfig doesn't build with it.

Bump the kernel to 4.19.204 release that contains a lot of
fixes for newer gcc.

Fixes:
https://gitlab.com/kubu93/buildroot/-/jobs/1525741062
https://gitlab.com/kubu93/buildroot/-/jobs/1525741060



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>