[liftoff][arm] Make context register allocatable

This will make it easier to generate builtin calls that require the
context to be passed in that register, because this can be represented
as a {LiftoffRegister} then.

R=thibaudm@chromium.org

Bug: v8:11453
Change-Id: I00995203cc936f23d1c01fdbf8f13eb929f228ae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2752151Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73345}

src/execution/arm/frame-constants-arm.h

@@ -76,8 +76,8 @@ class WasmCompileLazyFrameConstants : public TypedFrameConstants {
 // registers (see liftoff-assembler-defs.h).
 class WasmDebugBreakFrameConstants : public TypedFrameConstants {
  public:
-  // {r0, r1, r2, r3, r4, r5, r6, r8, r9}
-  static constexpr uint32_t kPushedGpRegs = 0b1101111111;
+  // {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9}
+  static constexpr uint32_t kPushedGpRegs = 0b1111111111;
   // {d0 .. d12}
   static constexpr int kFirstPushedFpReg = 0;
   static constexpr int kLastPushedFpReg = 12;

src/wasm/baseline/liftoff-assembler-defs.h

@@ -48,9 +48,9 @@ constexpr RegList kLiftoffAssemblerFpCacheRegs = DoubleRegister::ListOf(
 
 #elif V8_TARGET_ARCH_ARM
 
-// r7: cp, r10: root, r11: fp, r12: ip, r13: sp, r14: lr, r15: pc.
+// r10: root, r11: fp, r12: ip, r13: sp, r14: lr, r15: pc.
 constexpr RegList kLiftoffAssemblerGpCacheRegs =
-    Register::ListOf(r0, r1, r2, r3, r4, r5, r6, r8, r9);
+    Register::ListOf(r0, r1, r2, r3, r4, r5, r6, r7, r8, r9);
 
 // d13: zero, d14-d15: scratch
 constexpr RegList kLiftoffAssemblerFpCacheRegs = LowDwVfpRegister::ListOf(