crypto: caam - fix pkcs1pad(rsa-caam, sha256) failure because of invalid input

The problem is with the input data size sent to CAAM for encrypt/decrypt.
Pkcs1pad is failing due to pkcs1 padding done in SW starting with0x01
instead of 0x00 0x01.
CAAM expects an input of modulus size. For this we strip the leading
zeros in case the size is more than modulus or pad the input with zeros
until the modulus size is reached.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>