fsi: master-ast-cf: select GENERIC_ALLOCATOR

fsi: master-ast-cf: select GENERIC_ALLOCATOR

In randconfig builds without CONFIG_GENERIC_ALLOCATOR, this driver
fails to link:

ERROR: "gen_pool_alloc_algo" [drivers/fsi/fsi-master-ast-cf.ko] undefined!
ERROR: "gen_pool_fixed_alloc" [drivers/fsi/fsi-master-ast-cf.ko] undefined!
ERROR: "of_gen_pool_get" [drivers/fsi/fsi-master-ast-cf.ko] undefined!
ERROR: "gen_pool_free" [drivers/fsi/fsi-master-ast-cf.ko] undefined!

Select the dependency as all other users do.

Fixes: 6a794a27daca ("fsi: master-ast-cf: Add new FSI master using Aspeed ColdFire")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>