libipt: add a block cache to struct pt_section

Add an optional block cache to struct pt_section.  The cache is implicitly
created when the section is mapped and implicitly unmapped when the section is
destroyed.

Cache users need to keep the section mapped as long as they are using the cache.

Change-Id: I3f9c586ff62cdaf272c2b339710558122248b28a
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
7 files changed