simpleperf: better support kernel symbols when running as root.

Instead of asking user to `echo 0 >/proc/sys/kernel/kptr_restrict`,
do it automatically in simpleperf.

Bug: None.
Test: run simpleperf as root.
Test: run simpleperf_unit_test.
Change-Id: If31aa03b6e30afb925cbf58835536ed4c969a635
3 files changed