[SVE] ACLE: Fix builtins for svdup_lane_bf16 and svcvtnt_bf16_f32_x

bfloat16 variants of svdup_lane were missing, and svcvtnt_bf16_x
was implemented incorrectly (it takes an operand for the inactive
lanes)

Reviewers: fpetrogalli, efriedma

Reviewed By: fpetrogalli

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82908