[POWERPC] spufs: Remove ctx_info and ctx_info_list

Remove the ctx_info struct entirely, and also the ctx_info_list.  This
fixes a race where two processes can clobber each other's ctx_info structs.

Instead of using the list, we just repeat the search through the file
descriptor table.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>