crypto: qat - Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
ready to enable it globally.

Use the `__struct_group()` helper to separate the flexible array
from the rest of the members in flexible `struct qat_alg_buf_list`,
through tagged `struct qat_alg_buf_list_hdr`, and avoid embedding the
flexible-array member in the middle of `struct qat_alg_fixed_buf_list`.

Also, use `container_of()` whenever we need to retrieve a pointer to
the flexible structure.

So, with these changes, fix the following warnings:
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>