tools: ynl-gen: support sub-type for binary attributes

tools: ynl-gen: support sub-type for binary attributes

Sub-type annotation on binary attributes may indicate that the attribute
carries an array of simple types (also referred to as "C array" in docs).
Support rendering them as such in the C user code. For example for u32,
instead of:

  struct {
    u32 arr;
  } _len;

  void *arr;

render:

  struct {
    u32 arr;
  } _count;

  __u32 *arr;

Note that count is the number of elements while len was the length in bytes.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250509154213.1747885-2-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>