arch: Initial support for RX architecture support

This commit add require code for supporting RX architecture
to Zephyr, it include:
- Add require config and CMakelists for RX arch
- Intialization startup code for RX
- Interrupt and exception handling
- Thread creation adn thread context switch
- irq offload using SW interrupt

Signed-off-by: Duy Nguyen <duy.nguyen.xa@renesas.com>