drivers: boards: Merge HAS_DTS_SPI_PINS with HAS_DTS_SPI

Every board that uses dts-enabled spi drivers has a board-level dts, so
there is no need to have separate configs HAS_DTS_SPI_PINS and
HAS_DTS_SPI.

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