Anaconda always creates /etc/kernel/cmdline, even on GRUB+BLS installs, so
the previous if/else misdetected systemd-boot on GRUB systems: the IOMMU
arguments landed in /etc/kernel/cmdline after GRUB+BLS boot entries had
already been generated from it, and never reached the running kernel
(observed on thinkpad and nuc6i7kyb).
Instead of branching on one file, update every kernel-argument surface
idempotently, guarded by existence: /etc/kernel/cmdline (kernel-install
source for systemd-boot and GRUB+BLS future kernels), /etc/default/grub
(grub.cfg flows), and the options line of every already-generated
/boot/loader/entries/*.conf (same shape under both systemd-boot and
GRUB+BLS). Guard the nested=1 append as well.
Lukas Greve
cd4302cb09