PPC: Change store buffer overflow check to not rely on the store buffer being (2*Size) aligned.

Port 6a628573

Original commit message:
    This reduces the reserved virtual memory size needed for the store buffer.

R=ulan@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=chromium:578883
LOG=NO

Review URL: https://codereview.chromium.org/1848983002

Cr-Commit-Position: refs/heads/master@{#35186}

src/ppc/macro-assembler-ppc.cc

@@ -570,8 +570,7 @@ void MacroAssembler::RememberedSetHelper(Register object,  // For debug tests.
   StoreP(scratch, MemOperand(ip));
   // Call stub on end of buffer.
   // Check for end of buffer.
-  mov(r0, Operand(StoreBuffer::kStoreBufferMask));
-  and_(r0, scratch, r0, SetRC);
+  TestBitMask(scratch, StoreBuffer::kStoreBufferMask, r0);
 
   if (and_then == kFallThroughAtEnd) {
     bne(&done, cr0);