net: microchip: vcap: Add vcap_rule_get_key_u32

Add the function vcap_rule_get_key_u32 which allows to get the value and
the mask of a key that exist on the rule. If the key doesn't exist,
it would return error.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>