Fix stack imbalance in DA release

In OS_DynamicArea 2, a stack imbalance would occur if an error is
encountered while releasing the physical pages of a PMP (R1-R8 pushed,
but only R1-R7 pulled). Fix it, but also don't bother storing R1, since
it's never modified.

s/ChangeDyn

@@ -1332,7 +1332,7 @@ DAR_notsparse
         ; This is a bit of a simplistic approach - request for everything to
         ; be unmapped and leave it to PMP_LogOp to detect which pages are and
         ; aren't there
-        Push    "r1-r8"
+        Push    "r2-r8"
         LDR     r6, [r10, #DANode_Base]
         MOV     r3, #0
         LDR     r4, [r10, #DANode_SparseHWM] ; Assume HWM valid
@@ -1353,7 +1353,7 @@ DAR_PMP_logunmap
         MOV     r2, sp
         SWI     XOS_DynamicArea
         MOV     sp, r8
-        Pull    "r1-r8", VS
+        Pull    "r2-r8", VS
         EXIT    VS
         CMP     r4, #0
         MOV     r3, #0
@@ -1376,13 +1376,13 @@ DAR_PMP_physunmap
         MOV     r2, sp
         SWI     XOS_DynamicArea
         MOV     sp, r8
-        Pull    "r1-r7", VS
+        Pull    "r2-r8", VS
         EXIT    VS
         CMP     r4, #0
         MOV     r3, #0
         BGT     DAR_PMP_physloop
         ; All pages released, safe to free area
-        Pull    "r1-r8"
+        Pull    "r2-r8"
         MOV     r0, #DAReason_Remove
         B       DAR_delink
 DAR_notPMP