Export more files in proc_perf.

Export /proc/sys/kernel/perf_cpu_time_max_percent and
/proc/sys/kernel/perf_event_mlock_kb in proc_perf. So
they can be read in shell and written by init.

This is needed by simpleperf to control cpu percent and
memory used for profiling.

Bug: 110706031
Test: build and boot hikey960 successfully.

Change-Id: I2a01f583508003ab73427bab30a7982a27dfa677