crypto: caam - Provide the name of the function and provide missing descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/crypto/caam/caampkc.c:199: warning: expecting prototype for from a given scatterlist(). Prototype was for caam_rsa_count_leading_zeros() instead
 drivers/crypto/caam/caamalg_qi2.c:87: warning: Function parameter or member 'xts_key_fallback' not described in 'caam_ctx'
 drivers/crypto/caam/caamalg_qi2.c:87: warning: Function parameter or member 'fallback' not described in 'caam_ctx'

Cc: "Horia Geantă" <horia.geanta@nxp.com>
Cc: Aymen Sghaier <aymen.sghaier@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>