[ARM] Enable arm_legitimize_address for Thumb-2

[ARM] Enable arm_legitimize_address for Thumb-2

Currently arm_legitimize_address doesn't handle Thumb-2 at all, resulting in
inefficient code.  Since Thumb-2 supports similar address offsets use the Arm
legitimization code for Thumb-2 to get significant codesize and performance
gains.  SPECINT2006 shows 0.4% gain on Cortex-A57, while SPECFP improves 0.2%.

    gcc/
	* config/arm/arm.c (arm_legitimize_address): Remove Thumb-2 bailout.

From-SVN: r276961