Add reference to wc_AesInit in Gmac API doc

[embhorn]

Description

wc_GmacSetKey and wc_GmacUpdate doxygen examples should show using wc_AesInit to set the Aes devID.

Fixes zd14858

Testing

Documentation only

Checklist

• [ ] added tests
• [X] updated/added doxygen
• [ ] updated appropriate READMEs
• [ ] Updated manual and documentation