[RISCV][llvm-readobj,llvm-objdump] Use getRISCVVendorRelocationTypeName for RISCV vendor relocations (#172811)
Use getRISCVVendorRelocationTypeName to resolve RISCV vendor-specific
relocation names (R_RISCV_CUSTOM192-255) when preceded by
R_RISCV_VENDOR.
This improves the output of llvm-readobj and llvm-objdump to show
vendor-specific names like R_RISCV_QC_ABS20_U, R_RISCV_QC_E_BRANCH
(QUALCOMM) and R_RISCV_NDS_BRANCH_10 (ANDES) instead of generic
R_RISCV_CUSTOM* names.
Per RISC-V psABI, R_RISCV_VENDOR must be placed immediately before its
associated vendor-specific relocation, so the vendor symbol is consumed
after one use. Unknown vendors fall back to R_RISCV_CUSTOM*.