ARM: Add Ldrd/Strd to the macro assembler

ARM: Add Ldrd/Strd to the macro assembler

The macro assembler now checks for ARMv7 support and generates instructions for Ldrd/Strd accordingly. INstructions ldrd/strd in the assembler requires ARMv7 support enabled. This removes the a check for CAN_USE_ARMV7_INSTRUCTIONS making the ARMv7 support in the simulator fully controled by the --enable-armv7 flag.
Review URL: http://codereview.chromium.org/2226003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4726 ce2b1a6d-e550-0410-aec6-3dcde31c8c00