remoteproc: imx_dsp_rproc: Add custom memory copy implementation for i.MX DSP Cores

The IRAM is part of the HiFi DSP.
According to hardware specification only 32-bits write are allowed
otherwise we get a Kernel panic.

Therefore add a custom memory copy and memset functions to deal with
the above restriction.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Link: https://lore.kernel.org/r/20230221170356.27923-1-iuliana.prodan@oss.nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>