Add additional constants.

- Add constants for the fields in the root-entry table address register,
  namely the root type type (RTT) and root table address (RTA) mask.
- Add macros for the bitmask of the domain ID field in the second word
  of context table entries as well as a helper macro (DMAR_CTX2_GET_DID)
  to extract the domain ID from a context table entry.

Reviewed by:	kib
MFC after:	1 month
Sponsored by:	Chelsio Communications

sys/x86/iommu/intel_reg.h

@@ -67,7 +67,9 @@ typedef	struct dmar_ctx_entry {
 #define	DMAR_CTX2_AW_4LVL	2		/* 4-level page tables */
 #define	DMAR_CTX2_AW_5LVL	3		/* 5-level page tables */
 #define	DMAR_CTX2_AW_6LVL	4		/* 6-level page tables */
+#define	DMAR_CTX2_DID_MASK	0xffff0
 #define	DMAR_CTX2_DID(x)	((x) << 8)	/* Domain Identifier */
+#define	DMAR_CTX2_GET_DID(ctx2)	(((ctx2) & DMAR_CTX2_DID_MASK) >> 8)
 
 typedef struct dmar_pte {
 	uint64_t pte;
@@ -214,6 +216,8 @@ typedef struct dmar_irte {
 
 /* Root-Entry Table Address register */
 #define	DMAR_RTADDR_REG	0x20
+#define	DMAR_RTADDR_RTT	(1 << 11)	/* Root Table Type */
+#define	DMAR_RTADDR_RTA_MASK	0xfffffffffffff000
 
 /* Context Command register */
 #define	DMAR_CCMD_REG	0x28