arm7tdmi: clean up architecture definition

src/runtime/arch_arm.go

@@ -1,7 +1,9 @@
-// +build arm,!baremetal
+// +build arm,!baremetal arm,arm7tdmi
 
 package runtime
 
+import "device/arm"
+
 const GOARCH = "arm"
 
 // The bitness of the CPU (e.g. 8, 32, 64).
@@ -11,3 +13,7 @@ const TargetBits = 32
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3
 }
+
+func getCurrentStackPointer() uintptr {
+	return arm.ReadRegister("sp")
+}

src/runtime/runtime_arm7tdmi.go

@@ -3,14 +3,9 @@
 package runtime
 
 import (
-	"device/arm"
 	"unsafe"
 )
 
-const TargetBits = 32
-
-const GOARCH = "arm"
-
 type timeUnit int64
 
 const tickMicros = 1
@@ -82,10 +77,6 @@ func abort() {
 	}
 }
 
-func getCurrentStackPointer() uintptr {
-	return arm.ReadRegister("sp")
-}
-
 // Implement memset for LLVM and compiler-rt.
 //go:export memset
 func libc_memset(ptr unsafe.Pointer, c byte, size uintptr) {