RFR(S) 8075093: Enable UseFPUForSpilling support on SPARC

[Vladimir Kozlov]

https://bugs.openjdk.java.net/browse/JDK-8075093
http://cr.openjdk.java.net/~kvn/8075093/webrev

SPARC S3 core and beyond have single-cycle MOV instructions (MOVdTOx, 
MOVxTOd) for FP-to-GP and GP-to-FP register moves. These when used under 
UseFPUForSpilling can help improve performance.

Contributed-by: Shrinivas Joshi

I reviewed changes.