Refactor loading of /proc/kallsyms

Moves related functions to a new source file (kallsyms.cpp). Adds
support for the security.lower_kptr_restrict system property. The
implementation of ScopedKptrUnrestrict is based on Perfetto (see
aosp/1454882).

Test: lunch aosp_crosshatch-userdebug; atest CtsSimpleperfTestCases
Change-Id: Ie6ba7aab93d68be915583ad4f8551c627b35f292
14 files changed