typedefs.h: Move some typedefs to a separate file

typedefs.h: Move some typedefs to a separate file

The relationship between sinks, sources, cards, profiles, and ports
is becoming ever more intertwined, to the point that if you try to
include one file from the other, you're likely to end up with some
weird error somewhere else.

Work around this by creating a new typedefs.h, which does not depend
on anything else, and just creates a few typedefs.

(Can be expanded with more typedefs in the future if the need arises.)

Signed-off-by: David Henningsson <david.henningsson@canonical.com>