cxl: Refactor adaptor init/teardown

Some aspects of initialisation are done only once in the lifetime of
an adapter: for example, allocating memory for the adapter,
allocating the adapter number, or setting up sysfs/debugfs files.

However, we may want to be able to do some parts of the
initialisation multiple times: for example, in error recovery we
want to be able to tear down and then re-map IO memory and IRQs.

Therefore, refactor CXL init/teardown as follows.

 - Keep the overarching functions 'cxl_init_adapter' and its pair,
   'cxl_remove_adapter'.

 - Move all 'once only' allocation/freeing steps to the existing
   'cxl_alloc_adapter' function, and its pair 'cxl_release_adapter'
   (This involves moving allocation of the adapter number out of
   cxl_init_adapter.)

 - Create two new functions: 'cxl_configure_adapter', and its pair
   'cxl_deconfigure_adapter'. These two functions 'wire up' the
   hardware --- they (de)configure resources that do not need to
   last the entire lifetime of the adapter

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>