Reduce the number of separate SPI core requests when setting the UINC bit in
the TEF FIFO, and instead batch them up into a single SPI core request.

Link: https://lore.kernel.org/r/20201126132144.351154-6-mkl@pengutronix.deTested-by: NThomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>