Add more ZA modes (#77361)

Add more ZA modes
    
 Adds the arm_shared_za and arm_preserves_za attributes to the existing
 arm_new_za attribute. The functionality already exists in LLVM, so just
 "linking the pieces together".
    
For more details see:
https://arm-software.github.io/acle/main/acle.html#sme-attributes-relating-to-za