doc: fix kernel-parameters.txt mistaken deletions

Re-add missing kernel-parameters documentation that was accidentally
deleted in commit 0cb55ad2.

Thanks to Ingo and Weidong Han for the heads-up on this.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
cc: Ingo Molnar <mingo@elte.hu>
cc: Len Brown <lenb@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>