perfmon: Add support for multiplexers

This introduces a new struct nouveau_specmux with a couple (reg, val)
which can be used to define a mux.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
perfmon: Add complex hardware events for nva3 chipsets

All of these signals use multiplexers.

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