universal7870: fix gatekeeperd

gatekeeperd needs to run as group system otherwise
it will not be able to write into /efs/TEE

gatekeeperd HAS TO run in 32bit so we can use all PIE based blobs
and only these are working properly

this commit takes the current system/core/gatekeeperd and modifies
it to build 32bit (as gatekeeperd_32) by overriding gatekeeperd
(see Android.bp).
it also ensures the gatekeeperd.rc is correctly set and all needed
selinux policies are set

the whole setup has been tested in selinux=enforcing and fixes
the PIN/Password issues

Signed-off-by: steadfasterX <steadfasterX@gmail.com>