imx6: optimize for NEON FPU hardware

The IMX6 SoC uses an ARM Cortext-A9 which has both NEON and VFPv3 hardware
blocks.  This will tune gcc to use neon instead of vfpv3 which will outperform
VFPv3.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

SVN-Revision: 39760