arm64: defconfig: Enable DMA_RESTRICTED_POOL

Enable support for restricted DMA pools which provide a level of DMA
memory protection on systems with limited hardware protection
capabilities, such as those lacking an IOMMU.

For instance, mt8192-asurada-spherion makes use of this to provide a
restricted DMA region for WiFi since its MT7921E WiFi card is connected
through PCIe, and the MT8192 SoC doesn't have an IOMMU context for the
PCIe controller.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20230130200820.82084-2-nfraprado@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>