`error.c` and error.h are the more logical place to keep this code and it
prevents issues with building `common.c` and conflicts with other projects
that use mbedtls (such as mbedOS).
`error.c` has been automatically generated by first adding the code to
`error.fmt` and then running `./scripts/generate_errors.pl`.
Also add parenthesis to the addition in `MBEDTLS_ERR_ADD`.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
