lib/crypto: riscv: Move arch/riscv/lib/crypto/ into lib/crypto/

lib/crypto: riscv: Move arch/riscv/lib/crypto/ into lib/crypto/

Move the contents of arch/riscv/lib/crypto/ into lib/crypto/riscv/.

The new code organization makes a lot more sense for how this code
actually works and is developed.  In particular, it makes it possible to
build each algorithm as a single module, with better inlining and dead
code elimination.  For a more detailed explanation, see the patchset
which did this for the CRC library code:
https://lore.kernel.org/r/20250607200454.73587-1-ebiggers@kernel.org/.
Also see the patchset which did this for SHA-512:
https://lore.kernel.org/linux-crypto/20250616014019.415791-1-ebiggers@kernel.org/

This is just a preparatory commit, which does the move to get the files
into their new location but keeps them building the same way as before.
Later commits will make the actual improvements to the way the
arch-optimized code is integrated for each algorithm.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Palmer Dabbelt <palmer@dabbelt.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20250619191908.134235-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>