spi: atmel-quadspi: Add verbose debug facilities to monitor register accesses

spi: atmel-quadspi: Add verbose debug facilities to monitor register accesses

This feature should not be enabled in release but can be useful for
developers who need to monitor register accesses at some specific places.

Helped me identify a bug in u-boot, by comparing the register accesses
from the linux driver with the ones from its u-boot variant.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20200320065058.891221-1-tudor.ambarus@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>