cxl: Use radix__flush_all_mm instead of generic flush_all_mm

The generic implementation of this function isn't really generic (Hash
is not implemented). Unfortunately, the runtime warnings cannot be
replaced with BUILD_BUG's, so it seems safer not to provide a stub in
the first place.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221109045112.187069-6-bgray@linux.ibm.com