spi: spi-geni-qcom: Modify bus bw vote and DMA buffer mapping

Modify the bus bw vote to match the max frequency of the slave that the
current transfer is intended for.
The bus bw vote will impact performance of all data transfer modes.

Ensure that the dma mapping is done using the wrapper device using the
API exposed by the geni common driver.

Also select GSI DMA transfer mode if there are valid DMA channels.

Change-Id: I2f2f17d4839543e9ee994a4d85f9d2f364e17478
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>