Add public getter APIs for mbedtls_ecp_curve_info

[gabor-mezei-arm]

As part of #4683, as a result of reviewing the programs there are uses of MBEDTLS_PRIVATE fields of the mbedtls_ecp_curve_info structure. To avoid the access of the private fields create and use new public getter APIs for the fields of the mbedtls_ecp_curve_info structure.

Accessed flelds:

• name
• grp_id

Affected files:

• pkey/ecdsa.c
• pkey/gen_key.c
• ssl/ssl_server2.c

[gilles-peskine-arm]

#4842 made all the fields of mbedtls_ecp_curve_info public.