iommu/vt-d: Clean/document fault status flags

#define DMA_FECTL_IM (((u32)1) << 31)

/* FSTS_REG */

#define DMA_FSTS_PPF ((u32)2)

#define DMA_FSTS_PFO ((u32)1)

#define DMA_FSTS_IQE (1 << 4)

#define DMA_FSTS_ICE (1 << 5)

#define DMA_FSTS_ITE (1 << 6)

#define DMA_FSTS_PRO (1 << 7)

#define DMA_FSTS_PFO (1 << 0) /* Primary Fault Overflow */

#define DMA_FSTS_PPF (1 << 1) /* Primary Pending Fault */

#define DMA_FSTS_IQE (1 << 4) /* Invalidation Queue Error */

#define DMA_FSTS_ICE (1 << 5) /* Invalidation Completion Error */

#define DMA_FSTS_ITE (1 << 6) /* Invalidation Time-out Error */

#define DMA_FSTS_PRO (1 << 7) /* Page Request Overflow */

#define dma_fsts_fault_record_index(s) (((s) >> 8) & 0xff)

/* FRCD_REG, 32 bits access */