ti_config_fragments: am33xx_only: enable spidev module

* The spidev module is to be used to manage the spi0 interface in the
  am335x-boneblack-iot-cape device tree.

Signed-off-by: Jacob Stiffler <j-stiffler@ti.com>

ti_config_fragments/am33xx_only.cfg

@@ -17,3 +17,6 @@ CONFIG_CPUSETS=n
 
 # Increase CMA for HDMI
 CONFIG_CMA_SIZE_MBYTES=48
+
+# Enable spidev module
+CONFIG_SPI_SPIDEV=m