snippets: Organize snippets based on generality and vendors specific snippets

Snippets ideally should be general purpose and not limited to vendors or
specific boards. To distinguish between general snippets that can be
used in association with any target and those that are vendor specific,
create one more level and organize by vendors and put general ones under
generic.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif