Documentation: update panic parameter info

Add a little more info for some of the panic-related kernel parameters.
Fix "oops=panic" to fit in 80 columns.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>