rtl8735b: add plaintext-key AES-GCM device test alongside HUK, selected by devId

[dgarske]

Summary

Extends the AmebaPro2 RTL8735B HUK example (rtl8735b/) with a plaintext-key AES-GCM test that uses the new WOLFSSL_RTL8735B_AES crypto-callback device, registered alongside the HUK device and selected per Aes by devId. Companion to wolfSSL PR wolfSSL/wolfssl#10970 (required to build).

What it adds

• Enables WOLFSSL_RTL8735B_AES in user_settings.h and registers wc_Rtl8735b_AesRegister(WC_RTL8735B_AES_DEVID) next to wc_Rtl8735b_HukRegister(WC_HUK_DEVID).
• A plaintext AES-GCM check: reproduces a published McGrew GCM vector on the HW engine (key used verbatim), then encrypts the same 32 key bytes through both devices and shows the plaintext ciphertext differs from the HUK device-bound ciphertext -- demonstrating run-time selection by devId.

Testing

On the RealTek RTL8735B (AmebaPro2 EVB): 67/67 PASS, including the plaintext AES-GCM vector match and HUK coexistence.

wolfSSL/wolfssl#10970

[Copilot]

Pull request overview

Adds an optional second crypto-callback device for RTL8735B that exercises AES-GCM using a plaintext caller-supplied key (selected by devId) alongside the existing HUK-bound device, and documents/controls it via build settings.

Changes:

• Enable WOLFSSL_RTL8735B_AES in the RTL8735B example settings to compile plaintext-key AES tests.
• Add an AES-GCM known-answer test (published vector) plus a “coexistence” demonstration comparing ciphertext across the plaintext device vs HUK device.
• Document the new second-device behavior and selection mechanism (devId) in the RTL8735B README.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
rtl8735b/user_settings.h	Enables the plaintext-key AES device build flag alongside the existing HUK setup.
rtl8735b/README.md	Documents the second crypto-callback device and how devId selects plaintext vs HUK behavior.
rtl8735b/main.c	Implements plaintext-key AES-GCM KAT + coexistence demo and registers/unregisters the second device.

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