MAINTAINERS: Remove myself from PA Semi entries

The platform is old, very few users and I lack bandwidth to keep after
it these days.

Mark the base platform as well as the drivers as orphans, patches have
been flowing through the fallback maintainers for a while already.

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>