CCM interface changes: impact for alternative implementations
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The CCM interface has changed with the addition of support for
multi-part operations. Five new API functions have been defined:
mbedtls_ccm_starts(), mbedtls_ccm_set_lengths(),
mbedtls_ccm_update_ad(), mbedtls_ccm_update() and mbedtls_ccm_finish().
Alternative implementations of CCM (`MBEDTLS_CCM_ALT`) have now to
implement those additional five API functions.

Add migration guide for developers of CCM alternative implementation
Add migration guide for developers of CCM alternative implementation

Signed-off-by: Ronald Cron <b35ff5b7ca26c4ae9b66b92f2cf34224c8e26b08@arm.com>
