Intel SPI controller only has a 64 bytes FIFO. This adds a sanity
check before triggering any HW/SW sequencer work.

Additionally for the SW sequencer, if given data length is zero,
we should not mark the 'Data Cycle' bit.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>