Make /proc/kmsg and /proc/sysrq-trigger system-process-readable

This is so that the system process can capture kernel thread stacks when the
watchdog detects a deadlock.  Previously, /proc/kmsg was root/root and mode
0400, and /proc/sysrq-trigger was root/root and mode 0200.  With this
change, /proc/kmsg becomes root/system and 0440, and /proc/sysrq-trigger
becomes root/system and 0220.

Change-Id: Iac46bd10bd11d495024afeb5d693107ce5074791