On 32-bit platforms, float64 stack returns take 2 stack slots. In the
implemention of the kArmPeek instruction we assume that provided slot
index points to the first stack slot. However, due to an off-by-1 issue
the provided slot index pointed to the second stack slot. This CL fixes
the problem and generalizes an existing test which reproduces it.

R=v8-arm-ports@googlegroups.com

Change-Id: Ibb2fd8275cf912da064e2f863c2d64d2526caaac
Reviewed-on: https://chromium-review.googlesource.com/839761Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50291}