Add doc update for 4 filters which is missing in filter_scheduler.rst

DiskFilter
NumInstancesFilter
IoOpsFilter
PciPassthroughFilter
are missing in doc/source/devref/filter_scheduler.rst, add them.

DocImpact

Change-Id: I50868598c9769783e1677c9ec50abf031896af82
Closes-Bug: #1276575
Merge "Add doc update for 4 filters which is missing in filter_scheduler.rst"