Fix a few bugs in TDBStore and KV config

[davidsaada]

Description

This PR fixes a few bugs in TDBStore and KV config.

1. Don't initialize TDBStore if already initialized.
2. When reading a TDBStore record, make sure size calculation don't wrap around (can happen in a corrupt record).
3. Fix a few problems in KV config init and deinit logic.

Pull request type

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

[ciarmcom]

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

[adbridge]

@davidsaada is this for RC3 ?

[adbridge]

@dannybenor can someone review this please

[davidsaada]

is this for RC3 ?

@adbridge I think it better be. No show stoppers fixed here, but the missing init check (which may cause double init calls) isn't very nice.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

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