STM32F407VG: Add FLASH support

[adamheinrich]

Description

This enables Flash IAP (In-Application Programming) support for STM32F407VG on DISCO_F407VG and ARCH_MAX platforms.

Pull request type

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

[cmonr]

LGTM

[bcostm]

LGTM too. Did you run the Flash IAP tests ?

[jeromecoutant]

I have executed ST CI tests:

target	platform_name	test suite	result	elapsed_time (sec)	copy_method
DISCO_F407VG-ARM	DISCO_F407VG	tests-mbed_drivers-flashiap	OK	34.49	default
DISCO_F407VG-ARM	DISCO_F407VG	tests-mbed_hal-flash	OK	19.96	default
DISCO_F407VG-GCC_ARM	DISCO_F407VG	tests-mbed_drivers-flashiap	OK	35.33	default
DISCO_F407VG-GCC_ARM	DISCO_F407VG	tests-mbed_hal-flash	OK	20.68	default
DISCO_F407VG-IAR	DISCO_F407VG	tests-mbed_drivers-flashiap	OK	34.0	default
DISCO_F407VG-IAR	DISCO_F407VG	tests-mbed_hal-flash	OK	19.77	default

[cmonr]

Note: This PR is now a part of a rollup PR (#8694).

No further work is needed here, as once that PR is merged, this PR will also be closed and marked as merged.

If any more commits are made in this PR, this PR will remain open and have to go through CI on its own.