Fix Quick compiler "out of registers"

There are a few places in the Arm backend that expect to be
able to survive on a single temp register - in particular
entry code generation and argument passing.  However, in the
case of a very large frame and floating point ld/st, the
existing code could end up using 2 temps.

In short, if there is a displacement overflow we try to use
indexed load/store instructions (slightly more efficient).
However, there are none for floating point - so we ended up
burning yet another register to construct a direct pointer.
This CL detects this case and doesn't try to use the indexed
load/store mechanism for floats.

Fix for https://code.google.com/p/android/issues/detail?id=67349

Change-Id: I1ea596ea660e4add89fd4fddb8cbf99a54fbd343