The SSD16xx uses a separate pin to indicate if an SPI transfer is a
command or data. This means that driver needs to split most SPI
transactions into two distinct transactions, one for commands and one
for data. The driver currently doesn't request SPI_HOLD_ON_CS which
means that the chip select will be released momentarily between the
command and data phase.
Update the driver to request SPI_HOLD_ON_CS and SPI_LOCK_ON to lock
the bus and complete both phases of a command in one atomic operation.
Signed-off-by: Andreas Sandberg <andreas@sandberg.uk>
