cryptodev: reorganize asymmetric structs

cryptodev: reorganize asymmetric structs

This patch adds crypto uint typedef so adding comment
about byte-order becomes unnecessary.

It makes API comments more tidy, and consistent
with other asymmetric crypto APIs.

Additionally it reorganizes code that enums, externs
and forward declarations are moved to the top of the
header file making code more readable.

It removes also comments like co-prime constraint
from mod inv as it is natural mathematical constraint,
not PMD constraint.

Signed-off-by: Arek Kusztal <arkadiuszx.kusztal@intel.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>