drivers: boards: Merge HAS_DTS_I2C_DEVICE with HAS_DTS_I2C

Every board that uses dts-enabled i2c drivers has a board-level dts, so
there is no need to have separate configs HAS_DTS_I2C_DEVICE and
HAS_DTS_I2C.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>