drivers: modem: RSSI measurement for PPP link

This PR addresses radio signal stength measurement during
and before PPP session. The PR provides provides facility
of readout for both +CSQ and +CESQ versions depending
upon the modems. This PR follows the idea of rssi readout
of PR#35496. Additionally, reliable Cell info update
is also ensured.

Signed-off-by: Tahir Akram <mtahirbutt@hotmail.com>
3 files changed