Revert "arm64:lib: Use Linaro's memset routine to avoid using DC instruction"

This reverts commit f1851497.

We have used another workaround in remoteproc_core.c. We use ioremap()
to map the carveout memory. The proper way to handle it is to use iommu
which relies on SMMU.

Signed-off-by: Wendy Liang <jliang@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>