modem_celullar: simcom a76xx: optionally power on GNSS

Optionally power on the GNSS module of simcom a76xx during the chat init
script. This is necessary because it does not seem possible to power on the
GNSS once the modem is in CMUX mode. Configurable through
`CONFIG_MODEM_CELLULAR_POWER_ON_GNSS`.

Signed-off-by: Olivier Lalonde <o@syskall.com>

Author: olalonde

drivers/modem/Kconfig.cellular

@@ -63,4 +63,7 @@ config MODEM_CELLULAR_NEW_BAUDRATE_DELAY
 	default 100 if DT_HAS_U_BLOX_LARA_R6_ENABLED
 	default 300
 
+config MODEM_CELLULAR_POWER_ON_GNSS
+	bool "Power on the modem's GNSS module"
+	depends on DT_HAS_SIMCOM_A76XX_ENABLED
 endif

drivers/modem/modem_cellular.c

@@ -2076,6 +2076,13 @@ MODEM_CHAT_SCRIPT_CMDS_DEFINE(simcom_a76xx_init_chat_script_cmds,
 			      MODEM_CHAT_SCRIPT_CMD_RESP_NONE("AT", 100),
 			      MODEM_CHAT_SCRIPT_CMD_RESP_NONE("AT", 100),
 			      MODEM_CHAT_SCRIPT_CMD_RESP("ATE0", ok_match),
+			      #ifdef CONFIG_MODEM_CELLULAR_POWER_ON_GNSS
+			      /* Power on the GNSS module.
+			       * We need to do this early, otherwise it does not work when
+			       * doing it later (e.g. from a user pipe).
+			       */
+			      MODEM_CHAT_SCRIPT_CMD_RESP_MULT("AT+CGNSSPWR=1", allow_match),
+			      #endif
 			      MODEM_CHAT_SCRIPT_CMD_RESP("AT+CFUN=4", ok_match),
 			      MODEM_CHAT_SCRIPT_CMD_RESP("AT+CMEE=1", ok_match),
 			      MODEM_CHAT_SCRIPT_CMD_RESP("AT+CREG=1", ok_match),