ARM64: Instruction simplification for array accesses.

HArrayGet and HArraySet with variable indexes generate two
instructions on arm64, like

    add temp, obj, #data_offset
    ldr out, [temp, index LSL #shift_amount]

When we have multiple accesses to the same array, the initial `add`
instruction is redundant.

This patch introduces the first instruction simplification in the
arm64-specific instruction simplification pass. It splits HArrayGet
and HArraySet using the new arm64-specific IR HIntermediateAddress.
After that we run GVN again to squash the multiple occurrences of
HIntermediateAddress.

Change-Id: I2e3d12fbb07fed07b2cb2f3f47f99f5a032f8312
diff --git a/test/527-checker-array-access-split/info.txt b/test/527-checker-array-access-split/info.txt
new file mode 100644
index 0000000..9206804
--- /dev/null
+++ b/test/527-checker-array-access-split/info.txt
@@ -0,0 +1 @@
+Test arm64-specific array access optimization.