Rollup merge of #126530 - beetrees:f16-inline-asm-riscv, r=Amanieu

Add `f16` inline ASM support for RISC-V

This PR adds `f16` inline ASM support for RISC-V. A `FIXME` is left for `f128` support as LLVM does not support the required `Q` (Quad-Precision Floating-Point) extension yet.

Relevant issue: #125398
Tracking issue: #116909

`@rustbot` label +F-f16_and_f128

Author: workingjubilee