MIPS64: Fixed kGap value

Changed value of kGap constexpr from 32 to 128. Old value caused debugger/debug/debug-scopes test to fail

TEST=debugger/debug/debug-scopes

Bug: 
Change-Id: Ib805b84dce342b317b6cace3196fd1a9690e9d7a
Reviewed-on: https://chromium-review.googlesource.com/549928Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@imgtec.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@imgtec.com>
Cr-Commit-Position: refs/heads/master@{#46273}

src/mips64/assembler-mips64.h

@@ -2006,7 +2006,7 @@ class Assembler : public AssemblerBase {
   // the generated instructions. This is so that multi-instruction sequences do
   // not have to check for overflow. The same is true for writes of large
   // relocation info entries.
-  static constexpr int kGap = 32;
+  static constexpr int kGap = 128;
 
   // Repeated checking whether the trampoline pool should be emitted is rather
   // expensive. By default we only check again once a number of instructions