icsf: update list of numeric attributes

ICSF expects that numeric attributes are encoded using an specific ASN.1
syntax. This commit updates the list of attribute classes that are
considered numeric.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: better usage of handle helper functions

Add a new helper function to build a token handle based on its name.
Also replace redundant code with calls for existing helper functions.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: add a generic function for all ICSF services

Add the `icsf_call` function that can be used for any ICSF call. This
commit also removes the `icsf_create` function replacing it with
`icsf_call` calls.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: remove `icsf_destroy` function

Removes the `icsf_destroy` function replacing it with `icsf_call` calls.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: update `icsf_list` to use `icsf_call`

Update the generic listing function to use `icsf_call` and to reduce
duplicated code.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: add support for symmetric key generation

Add a new function `icsf_generate_secret_key` that calls the CSFPGSK
service to create a key.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>