selftests/bpf: Work around llvm stack overflow in crypto progs

selftests/bpf: Work around llvm stack overflow in crypto progs

clang 23 fails to build crypto_bench.c and crypto_sanity.c with
"BPF stack limit exceeded". The progs fill a 408-byte
bpf_crypto_params on the stack and pass it to bpf_crypto_ctx_create().
clang 23 copies the byte-aligned cipher/key globals into it one byte at
a time through the stack, and keeps more than one copy of the struct
around. Together that blows the 512-byte limit.

Align the source arrays to 8 bytes so the copy is word-wise, and move
params off the stack into a static .bss var. static keeps it out of the
skeleton, where bpf_crypto_params is an incomplete type. Either change
alone is not enough.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>