Hello,
Yes, it goes in the extras line before the \n:
like
tftpboot::linux_model { 'el7_x86_64':
kernel => 'centos-7-x86_64/vmlinuz',
initrd => 'centos-7-x86_64/initrd.img',
ks => "
https://ksserver/ks/pupclient_x86_64.cfg",
extra => "inst.noverifyssl ksdevice=bootif simp_disk_crypt\nipappend 2"