Clean up the alloc_io_space() function by moving most of it to
the actual resource_ops. This allows for a bit less re-directions.
Future cleanups will follow, and will make up for the code
duplication currently present between rsrc_iodyn and rsrc_nonstatic
(which are hardly ever built at the same time anyway, therefore no
increase in built size).
Signed-off-by: NDominik Brodowski <linux@dominikbrodowski.net>