fsldma: Fix the DMA halt when using DMA_INTERRUPT async_tx transfer.

The DMA_INTERRUPT async_tx is a NULL transfer, thus the BCR(count register)
is 0. When the transfer started with a byte count of zero, the DMA
controller will triger a PE(programming error) event and halt, not a normal
interrupt. I add special codes for PE event and DMA_INTERRUPT
async_tx testing.

Signed-off-by: Zhang Wei <wei.zhang@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/dma/fsldma.h b/drivers/dma/fsldma.h
index ba78c42..fddd6ae 100644
--- a/drivers/dma/fsldma.h
+++ b/drivers/dma/fsldma.h
@@ -40,6 +40,7 @@
 #define FSL_DMA_MR_EOTIE	0x00000080
 
 #define FSL_DMA_SR_CH		0x00000020
+#define FSL_DMA_SR_PE		0x00000010
 #define FSL_DMA_SR_CB		0x00000004
 #define FSL_DMA_SR_TE		0x00000080
 #define FSL_DMA_SR_EOSI		0x00000002