API changes
   * Move alt helpers and definitions.
     Various helpers and definitions available for use in alt implementations
     have been moved out of the include/ directory and into the library/
     directory. The files concerned are ecp_internal.h and rsa_internal.h
     which have also been renamed to ecp_alt.h and rsa_alt_helpers.h
     respectively.

Add changelog entry for alt implementors
Add changelog entry for alt implementors

Files available for use by alt implementations have been moved and renamed
so alt implementators should be told about the changes specific to them.

Signed-off-by: Chris Jones <cbf609b812bf58762ceb89e8692559dbbe9149ea@arm.com>
