tests: i2c: add support for i2c sci-b on Renesas RA boards

Add Renesas RA board support for i2c test use sci_b_i2c:
- tests/drivers/i2c/i2c_api

Example for i2c use sci_b_i2c:

west build -b ek_ra8m1 tests/drivers/i2c/i2c_api/ -p always \
 -DDTC_OVERLAY_FILE=boards/ek_ra8m1_sci_b_i2c.overlay \
 -DCONF_FILE="boards/ek_ra8m1_sci_b_i2c.conf"

Signed-off-by: Khoa Tran <khoa.tran.yj@bp.renesas.com>
Signed-off-by: Thao Luong <thao.luong.uw@renesas.com>