ART: Relax GetInstructionSetFromString

Do not abort on an unknown instruction set string. Instead return
kNone and let the caller handle this.

Also simplify the patchoat tool to use this.

Bug: 17136416

(cherry picked from commit aabbb2066a715b3fd8e752291f74c6d77b970450)

Change-Id: I24131914bcf91c04ae93179bf809a2907f1f2b7a
6 files changed