eal: fix power intrinsics API description

eal: fix power intrinsics API description

Currently, the intrinsics documentation refers to `rte_cpu_get_features`
as a check for whether these intrinsics are supported at runtime. This
is incorrect, because actually the user should use the
`rte_cpu_get_intrinsics_support` API to do said check. Fix the typo.

Fixes: 128021421256 ("eal: add intrinsics support check infrastructure")

Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Liang Ma <liang.j.ma@intel.com>