crypto: caam - move DMA mask selection into a function

Exactly the same code to figure out DMA mask is repeated twice in the
driver code. To avoid repetition, move that logic into a standalone
subroutine in intern.h. While at it re-shuffle the code to make it
more readable with early returns.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Cc: Chris Spencer <christopher.spencer@sea.co.uk>
Cc: Cory Tusar <cory.tusar@zii.aero>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Horia Geantă <horia.geanta@nxp.com>
Cc: Aymen Sghaier <aymen.sghaier@nxp.com>
Cc: Leonard Crestez <leonard.crestez@nxp.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>