perfmon: Remove unused nouveau_perfsig_wrap() function

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
perfmon: Add support for multiplexers

This will allow us to configure complex hardware events using up to 8
multiplexers. The maximum number of multiplexers that can be set is
absolutely arbitrary.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>