genfstab: remove obsolete check for overlapping modes

1f03775f4f introduced arbitrary tag identification which removed the
variables this conditional checks.
genfstab: check sooner for pseudofs types
track_mount: lazily initialize track_mount trap/storage
api_fs_mount: mount sysfs read-only
common: introduce mount_conditionally

This is potentially evil, but we're using hand crafted input to eval
which should be safe. Use this to bind mount the chroot dir if it isn't
already a mount point.
common: mount /sys/firmware/efi/efivars if available
common: quote conditional for efivar mount

Prevents failures when the chroot base contains whitespace.