RISC-V/zfh: Support .float16 directive for assembler.

This probably need to be sent to mainline rather than here.

gas/
    * config/tc-riscv.c (FLT_CHARS): Added h and H.
    (riscv_pseudo_table): Added .float16.
    * read.c (hex_float): Handle case 'h' and 'H'.
    * testsuite/gas/riscv/extended/extended.exp: Updated.
    * testsuite/gas/riscv/extended/float16.d: New testcase.
    * testsuite/gas/riscv/extended/float16.s: Likewise.
5 files changed