spi: atmel: Remove AVR32 leftover

AV32 support has been from the kernel a few release ago, but there was
still some specific macro for this architecture in this driver. Lets
remove it.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20190919154034.7489-1-gregory.clement@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>