toolchain: musl: add riscv32/64 support

toolchain: musl: add riscv32/64 support

Don't switch the riscv64 target from glibc yet, there are known
issues with libblobmsg_json.so blowing up.

[    0.890000] This architecture does not have kernel memory protection.
[    0.900000] Run /sbin/init as init process
Error loading shared library libjson-c.so.2: Symbolic link loop (needed by /sbin
/init)
Error loading shared library libjson-c.so.2: Symbolic link loop (needed by /lib/
libblobmsg_json.so)
Error relocating /lib/libblobmsg_json.so: json_object_get_object: symbol not fou
nd
Error relocating /lib/libblobmsg_json.so: json_object_from_file: symbol not foun
d
Error relocating /lib/libblobmsg_json.so: json_tokener_parse: symbol not found
Error relocating /lib/libblobmsg_json.so: json_object_get_int: symbol not found
Error relocating /lib/libblobmsg_json.so: json_object_get_boolean: symbol not fo
und

Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>