spi: qup: allow block mode to generate multiple transactions

This let's you write more to the SPI bus than 64K-1 which is important
if the block size of a SPI device is >= 64K or some other device wants
to do something larger.

This has the benefit of completely removing spi_message from the spi-qup
transactions

Signed-off-by: Matthew McClintock <mmcclint@codeaurora.org>
Signed-off-by: Varadarajan Narayanan <varada@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>