Fix a bug in the description of the "p6-div" event. [1]

Update the description of the "p6-div" and "p6-mul" events according
to the "Intel(r) 64 and IA-32 Architectures Software Developers
Manual Volume 3B: System Programming Guide, Part 2, November 2006".

Reported by: Harald Servat <redcrash at gmail dot com> [1]