Add SELinux Policy for RILD to access FSG partition

Cherry-pick of commit 61191ea97e3d2172fe853061ba093d54b55ad95a

QCRIL has to access FSG partition which contains the MCFG MBN files
for downloading to modem.

Bug: 18487207

Change-Id: I628653a9f1593151efe5db39832cadf7d77a5475