ARM: Port instr simplification of array accesses.

After changing the addressing mode for array accesses (in
https://android-review.googlesource.com/248406) the 'add'
instruction that calculates the base address for the array can be
shared across accesses to the same array.

Before https://android-review.googlesource.com/248406:
    add IP, r[Array], r[Index0], LSL #2
    ldr r0, [IP, #12]
    add IP, r[Array], r[Index1], LSL #2
    ldr r0, [IP, #12]

Before this CL:
    add IP. r[Array], #12
    ldr r0, [IP, r[Index0], LSL #2]
    add IP. r[Array], #12
    ldr r0, [IP, r[Index1], LSL #2]

After this CL:
    add IP. r[Array], #12
    ldr r0, [IP, r[Index0], LSL #2]
    ldr r0, [IP, r[Index1], LSL #2]

Link to the original optimization:
    https://android-review.googlesource.com/#/c/127310/

Test: Run ART test suite on Nexus 6.
Change-Id: Iee26f9a0a7ca46abb90e3f60d19d22dc8dee4d8f