cannon arch: move derivable stuff to arch.go (#13350)

* cannon arch: move derivable stuff to arch.go

* address comments

cannon/mipsevm/arch/arch.go

+package arch
+
+// This file contains stuff common to both arch32 and arch64
+
+const (
+	IsMips32      = WordSize == 32
+	WordSizeBytes = WordSize >> 3
+	PageAddrSize  = 12
+	PageKeySize   = WordSize - PageAddrSize
+
+	MemProofLeafCount = WordSize - 4
+	MemProofSize      = MemProofLeafCount * 32
+)

cannon/mipsevm/arch/arch32.go

@@ -13,16 +13,8 @@ type (
 )
 
 const (
-	IsMips32      = true
-	WordSize      = 32
-	WordSizeBytes = WordSize >> 3
-	PageAddrSize  = 12
-	PageKeySize   = WordSize - PageAddrSize
-
-	MemProofLeafCount = 28
-	MemProofSize      = MemProofLeafCount * 32
-
 	AddressMask = 0xFFffFFfc
+	WordSize    = 32
 	ExtMask     = 0x3
 
 	HeapStart       = 0x05_00_00_00

cannon/mipsevm/arch/arch64.go

@@ -13,16 +13,8 @@ type (
 )
 
 const (
-	IsMips32      = false
-	WordSize      = 64
-	WordSizeBytes = WordSize >> 3
-	PageAddrSize  = 12
-	PageKeySize   = WordSize - PageAddrSize
-
-	MemProofLeafCount = 60
-	MemProofSize      = MemProofLeafCount * 32
-
 	AddressMask = 0xFFFFFFFFFFFFFFF8
+	WordSize    = 64
 	ExtMask     = 0x7
 
 	// Ensure virtual address is limited to 48-bits as many user programs assume such to implement packed pointers