configs/qemu_*: bump kernel version to 5.4.42

configs/qemu_*: bump kernel version to 5.4.42

In order to allow testing gcc 10 using those defconfig, bump to kernel 5.4.42
since it include some patches fixing some issue introduced by gcc 10.

For example:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10cfaa7456d70696a89d423ce1cb0fd22967773a
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8f6a84167e8618333d84ea4143812e3e74ced7da

All defconfig using a specific kernel version (csky, risc32) are not
taken into account.

Build and runtime tested: https://gitlab.com/kubu93/buildroot/pipelines/148390943

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>