eal: control max SIMD bitwidth

eal: control max SIMD bitwidth

This patch adds a max SIMD bitwidth EAL configuration. The API allows
for an app to set this value. It can also be set using EAL argument
--force-max-simd-bitwidth, which will lock the value and override any
modifications made by the app.

Each arch has a define for the default SIMD bitwidth value, this is used
on EAL init to set the config max SIMD bitwidth.

Signed-off-by: Ciara Power <ciara.power@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Ray Kinsella <mdr@ashroe.eu>