tests/qtest: Add ASPEED SBC ECDSA engine test

Add a qtest for the ASPEED secure boot controller ECDSA engine. It stages
the public key, signature and SHA-384 digest of a secp384r1 known-answer
vector (from the Linux kernel crypto self-test manager,
ecdsa_nist_p384_tv_template) into the SEC SRAM, triggers the engine's
verify command and checks the status register: a valid signature reports
done + pass, and a tampered signature reports done without pass.

The test is skipped when the crypto backend does not support ECDSA, via
qcrypto_akcipher_supports().

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260901085238.995968-10-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>