allow system_server to read device_config_reset_performed_prop

system server reads this property to keep track of whether server
configurable flags have been reset during current boot.
system server needs this information to decide whether to perform
following disaster recovery actions on framework level.

the get_prop added in this cl in system_server.te is not grouped
in the same place as the set_prop in system_server.te in another
cl (https://android-review.googlesource.com/c/platform/system/sepolicy/+/828284).
This is because these 2 properties are serving for different purposes:
device_config_flags_health_check_prop is used to control features(so will be
all the future set_prop added by other feature teams under "# server configurable flags properties"),
while device_config_reset_performed_prop is used by our API's internal implementation.
So I feel like it might be clearer if I put this get_prop in a different place rather than
appending to "# server configurable flags properties".

Test: build suceeded.

Change-Id: I64379aa8f0bbe093969b98d62093696a32aabe59