Revert "Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()""

This reverts commit b7d9aae4.

With the Qualcomm remoteproc driver now modified to use a carveout
memory region in 57f72170 ("remoteproc: qcom_q6v5_mss: Use a
carveout to authenticate modem headers"), we can reinstate c44094ee


("arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()")
which relaxes the arm64 implementation of arch_dma_prep_coherent() to
perform only a data cache clean operation, rather than a
clean-and-invalidate.

Signed-off-by: Will Deacon <will@kernel.org>