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

Add board support for EK_RA6M5, EK_RA6M4 i2c test use sci_i2c:
- tests/drivers/i2c/i2c_api

Example for i2c use sci_i2c:

west build -b ek_ra6m5 tests/drivers/i2c/i2c_api/ -p always \
 -DDTC_OVERLAY_FILE=boards/ek_ra6m5_sci_i2c.overlay \
 -DCONF_FILE="boards/ek_ra6m5_sci_i2c.conf"

Signed-off-by: Khai Cao <khai.cao.xh@renesas.com>
5 files changed