DISCO_L4R9I: update default STMOD+ pin

[jeromecoutant]

Description

Tested with Quectel BG96 expansion board on STMOD+ connector of L4R9I DISCO board.

NB: mbed_app.json:

    "target_overrides": {
        "DISCO_L4R9I": {
            "stmod_cellular.provide-default": "true", 
            "target.components_add": [
                "STMOD_CELLULAR"
            ]
        }, 

target	platform_name	test suite	result	elapsed_time (sec)	copy_method
DISCO_L4R9I-ARMC6	DISCO_L4R9I	features-cellular-tests-api-cellular_device	OK	50.26	default
DISCO_L4R9I-ARMC6	DISCO_L4R9I	features-cellular-tests-api-cellular_information	OK	24.05	default
DISCO_L4R9I-ARMC6	DISCO_L4R9I	features-cellular-tests-api-cellular_network	OK	66.38	default
DISCO_L4R9I-ARMC6	DISCO_L4R9I	features-cellular-tests-api-cellular_sms	OK	33.77	default
DISCO_L4R9I-ARMC6	DISCO_L4R9I	features-cellular-tests-socket-udp	OK	32.84	default

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

@LMESTM

Release Notes

[ciarmcom]

@jeromecoutant, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[bulislaw]

Was it wrong before?

[jeromecoutant]

Was it wrong before?

Yes, not tested :-(

[jeromecoutant]

Please, don't start CI yet,
need to double check some new information I have
Thx

[jeromecoutant]

Hi
Correction is now OK.
(mistake was only with STMOD 2 and 3 pins, they are by default mapped to UART tx and rx,
whereas STMOD 4 pins is not mapped to UART rts)

[adbridge]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts