Encapsulate cmake asn1c call, suppress useless output

Encapsulate the asn1c call from cmake in a cmake function run_asn1c(). As a notable change to the previous manual add_custom_command() invocation, in suppresses the output of asn1c by default [1] and stores it in a log file. In case of asn1c4 error, the output will output on stdout.

Use the new run_asn1c() in all occasions for code generation.

[1] it is quite verbose, with many warnings that we cannot influence nor suppress, and lists all generated files which is verified by the build system automatically, anyway.