[AVR32] Define ARCH_KMALLOC_MINALIGN to L1_CACHE_BYTES

This allows SLUB debugging to be used without fear of messing up DMA
transfers. SPI is one example that easily breaks without this patch.
Signed-off-by: NHaavard Skinnemoen <hskinnemoen@atmel.com>

include/asm-avr32/cache.h

@@ -4,6 +4,15 @@
 #define L1_CACHE_SHIFT 5
 #define L1_CACHE_BYTES (1 << L1_CACHE_SHIFT)
 
+/*
+ * Memory returned by kmalloc() may be used for DMA, so we must make
+ * sure that all such allocations are cache aligned. Otherwise,
+ * unrelated code may cause parts of the buffer to be read into the
+ * cache before the transfer is done, causing old data to be seen by
+ * the CPU.
+ */
+#define ARCH_KMALLOC_MINALIGN	L1_CACHE_BYTES
+
 #ifndef __ASSEMBLER__
 struct cache_info {
 	unsigned int ways;