Add support for vector maximum/minimum using Altivec instructions
VMAXSB, VMAXSH, VMAXSW, VMAXUB, VMAXUH, VMAXUW, and
VMINSB, VMINSH, VMINSW, VMINUB, VMINUH, VMINUW.
Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>