ARM: Use the shifter operand to merge in previous shift instructions.

When possible, we transform sequences of code of the form
    lsl r1, r2, #imm
    add r0, r5, r1
into
    add r0, r5, r2 LSL #imm

This is an adaptation of r21161.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/312173002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22017 ce2b1a6d-e550-0410-aec6-3dcde31c8c00