Telephony: Decode SPN from RuimRecords properly

To address issues with incorrect encoding scheme programmed
in some commercial CSIM cards, the decoded SPN is checked to
have characters in printable ASCII range. If not, they are
decoded with ENCODING_GSM_7BIT_ALPHABET scheme.

Change-Id: I938f4ac7d2c4cee6732c3abad1be7db7395276ad
CRs-Fixed: 483975