dma: Introduce generic dma_addr_*crypted helpers

AMD SME added __sme_set/__sme_clr primitives to modify the DMA address for
encrypted/decrypted traffic. However this doesn't fit in with other models,
e.g., Arm CCA where the meanings are the opposite. i.e., "decrypted" traffic
has a bit set and "encrypted" traffic has the top bit cleared.

In preparation for adding the support for Arm CCA DMA conversions, convert the
existing primitives to more generic ones that can be provided by the backends.
i.e., add helpers to
 1. dma_addr_encrypted - Convert a DMA address to "encrypted" [ == __sme_set() ]
 2. dma_addr_unencrypted - Convert a DMA address to "decrypted" [ None exists today ]
 3. dma_addr_canonical - Clear any "encryption"/"decryption" bits from DMA
    address [ SME uses __sme_clr() ] and convert to a canonical DMA address.

Since the original __sme_xxx helpers come from linux/mem_encrypt.h, use that
as the home for the new definitions and provide dummy ones when none is provided
by the architectures.

With the above, phys_to_dma_unencrypted() uses the newly added dma_addr_unencrypted()
helper and to make it a bit more easier to read and avoid double conversion,
provide __phys_to_dma().

Suggested-by: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: 42be24a4178f ("arm64: Enable memory encrypt for Realms")
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250227144150.1667735-3-suzuki.poulose@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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