mmc: core: Store pointer to bio_crypt_ctx in mmc_request

Make 'struct mmc_request' contain a pointer to the request's
'struct bio_crypt_ctx' directly, instead of extracting a 32-bit DUN from
it which is a cqhci-crypto specific detail.

This keeps the cqhci crypto specific details in the cqhci module, and it
makes mmc_core and mmc_block ready for MMC crypto hardware that accepts
the DUN and/or key in a way that is more flexible than that which will
be specified by the eMMC v5.2 standard.  Exynos SoCs are an example of
such hardware, as their inline encryption hardware takes keys directly
(it has no concept of keyslots) and supports 128-bit DUNs.

Note that the 32-bit DUN length specified by the standard is very
restrictive, so it is likely that more hardware will support longer DUNs
despite it not following the standard.  Thus, limiting the scope of the
32-bit DUN assumption to the place that actually needs it is warranted.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20210721154738.3966463-1-ebiggers@kernel.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>