[AArch64][SVE] Asm: Report SVE parsing diagnostics only once

Summary:
Prevent an issue where a diagnostic is reported multiple times by bailing out with a ParseFail if an invalid SVE register element qualifier/suffix is specified, for example:

 <stdin>:10:18: error: invalid sve vector kind qualifier
 add z20.h, z2.h, z31.x
                 ^
 <stdin>:10:18: error: invalid sve vector kind qualifier
 add z20.h, z2.h, z31.x
 
 ...
 
 <stdin>:10:18: error: invalid sve vector kind qualifier
 add z20.h, z2.h, z31.x
                 ^


Reviewers: fhahn, rengolin

Reviewed By: rengolin

Subscribers: aemerson, javed.absar, tschuett, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D39894

llvm-svn: 318297