The VRSAVE feature of the Altivec unit can be used to reduce the amount of
Altivec registers which need to be saved/restored during interrupt processing
and context switches.
In order to use the VRSAVE optimization a corresponding multilib (-mvrsave) is
required, see GCC configuration. The -mvrsave option must be added to the
ABI_FLAGS of the BSP.
Currently only the -mcpu=e6500 based QorIQ BSP support this optimization.
Update #4712.
