sepolicy : Allow mm-pp-daemon access to diag

The access to diag was restricted as part of this commit
'sepolicy: Restrict diag access available to domains'. This
prevents mm-pp-daemon from accessing diag which results in
failure of QDCM PC tool connection with the device/pp-daemon.
To resolve this, allow mm-pp-daemon r/w access to diag.

CRs-Fixed: 1077354
Change-Id: I10388ef8cf5855d12a7053bbffffdb70a3ba162b