acl: rework classify method selection

acl: rework classify method selection

Right now ACL library determines best possible (default) classify method
on a given platform with special constructor function rte_acl_init().
This patch makes the following changes:
 - Move selection of default classify method into a separate private
   function and call it for each ACL context creation (rte_acl_create()).
 - Remove library constructor function
 - Make rte_acl_set_ctx_classify() to check that requested algorithm
   is supported on given platform.

The purpose of these changes to improve and simplify algorithm selection
process and prepare ACL library to be integrated with the
max SIMD bitwidth series in discussion.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>