Bootloader support missing for DISCO_F746NG

[screamerbg]

Description

While trying to compile for DISCO_F746NG, the build system reports that the target doesn't have bootloader support. This is very surprising as NUCLEO_F746ZG (based on the same chip) has bootloader support and I'm able to successfully run firmware update on it.

See below:

$ mbed test -t ARM -m DETECT -n simple-mbed-cloud-client-tests-dev_mgmt*
[mbed] Working path "D:\Work\smcc-tests" (program)
[mbed] Detected "DISCO_F746NG" connected to "E:" and using com port "COM5"
Building library mbed-build (DISCO_F746NG, ARM)
Scan: smcc-tests
Bootloader not supported on this target.

CC @ARMmbed/team-st-mcd

Issue request type

[ ] Question
[X] Enhancement
[ ] Bug

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-189