pru_speak: fix dma mask

Hint from kumar.abhishek.kakkar@gmail.com who also informed me that
Deepak Karki did start the work of doing the integration to the shared
driver at https://github.com/deepakkarki/pruspeak/tree/pru_rproc_ps/src/driver.
Add DTS for PRUSPEAK

Signed-off-by: Jason Kridner <jdk@ti.com>