Explicitly allow system_server to (m)map data files

Linux kernel 4.14+ SELinux starts explicit map
permission check for file mmap operations.  Add this
permission to system_server for data file access,
which is used in scenario such as "adb install" of
APK's.

test: no longer see SELinux map denial on "adb install"
Change-Id: Id6016dd0b3f15dfdb0f02509ea812dee61ac78ed