crypto: caam - incapsulate dropping leading zeros into function

This function will be used into further patches.

Signed-off-by: Radu Alexe <radu.alexe@nxp.com>
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>