This patch adds a utility class that will be used in subsequent patches
for parsing the function/callsite attributes and determining whether
changes to PSTATE.SM are needed, or whether a lazy-save mechanism is
required.
It also implements some of the restrictions on the SME attributes
in the IR Verifier pass.
More details about the SME attributes and design can be found
in D131562.
Reviewed By: david-arm, aemerson
Differential Revision: https://reviews.llvm.org/D131570
Sander de Smalen