isdn: kcapi: don't build unused procfs code

The procfs file is completely unused without CONFIG_PROC_FS but causes
a compile time warning:

drivers/isdn/capi/kcapi_proc.c:97:36: error: unused variable 'seq_controller_ops' [-Werror,-Wunused-const-variable]
static const struct seq_operations seq_controller_ops = {
drivers/isdn/capi/kcapi_proc.c:104:36: error: unused variable 'seq_contrstats_ops' [-Werror,-Wunused-const-variable]
drivers/isdn/capi/kcapi_proc.c:179:36: error: unused variable 'seq_applications_ops' [-Werror,-Wunused-const-variable]
drivers/isdn/capi/kcapi_proc.c:186:36: error: unused variable 'seq_applstats_ops' [-Werror,-Wunused-const-variable]

Remove the file from the build in that config and make the calls into
it conditional instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240403080702.3509288-27-arnd@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>