eal/ppc: undefine AltiVec keyword vector

eal/ppc: undefine AltiVec keyword vector

The AltiVec header file is defining "vector", except in C++ build.
The keyword "vector" may conflict easily.
As a rule, it is better to use the alternative keyword "__vector".

The DPDK header file rte_altivec.h takes care of undefining "vector",
so the applications and dependencies are free to define the name "vector".

This is a compatibility breakage for applications which were using
the keyword "vector" for its AltiVec meaning.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Tested-by: Ali Alnubani <alialnu@nvidia.com>
Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
Acked-by: Ray Kinsella <mdr@ashroe.eu>