driver: serial: rz: Fix serial issue with sci and scif

Fix issues that Renesas RZ boards cannot run the below serial
samples properly with sci and scif.

- `samples/subsys/console/echo`
- `samples/subsys/shell/shell_module`

The modification is to make the callback invoked in tei interrupt.

Signed-off-by: Nhut Nguyen <nhut.nguyen.kc@renesas.com>