JSC ARM traditional failing on Octane NavierStokes test

https://bugs.webkit.org/show_bug.cgi?id=115626

Reviewed by Zoltan Herczeg.

Change the ARM traditional assembler to use double precision on value
conversions.

* assembler/ARMAssembler.h:

Change-Id: I2fbf6323a59120b497215696e10a1582ff927347
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149601 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>