AtPhonebook handleCpbsCommand was incorrectly sending two responses
to some requests (one inside the swtich statement, then repeating it
after breaking out of the switch statement).
This broke phonebook sync with Audi 2G MMI car kit.
Signed-off-by: Nigel Hannam <nigel@hannam.eu>

Change-Id: I65e54400aad2413725469951899d041870691369
Fix another duplicate response bug in AT+CSCS handling.

Also use the code flow of AT+CSCS/AT+CBPS for AT+CBPR handling.

Change-Id: I7d5b4d4d52b190f33784779d5f4dee27b22c23c9