sm4.c: use the common GHASH path for SM4-GCM on ARM assembly builds

[SparkiDev]

Fix the SM4-GCM usage of GMULT().
Fix sm4_gcm_calc_h too.

[SparkiDev]

PR for:
wolfSSL/wolfssl#11689

[Copilot]

🟡 Changes recommended

The affected ARM assembly path lacks automated coverage for the corrected GHASH behavior.

1 open finding

• Add AArch64 CI coverage for ARM SM4-GCM assembly behavior · New

What changed in this PR

Updates SM4-GCM to use the common GHASH implementation consistently across ARM assembly and other builds.

Changes:

• Keeps the GCM hash key unreflected.
• Removes redundant ARM-specific GMULT() operations.
• Uses common GHASH logic for nonce and tag calculations.

File	Description
sm4.c	Corrects SM4-GCM hash-key setup and GHASH usage.

🧠 Review effort: Balanced

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[Copilot]

🔵 Needs a closer look

The cryptographic representation changes are coherent and covered by new CI, but warrant final human validation across supported wolfSSL versions.

0 open findings

1 resolved since last review

• Add AArch64 CI coverage for ARM SM4-GCM assembly behavior

🧠 Review effort: Balanced