RISC-V: Support assembler modifier %got_pcrel_hi. gas/ * config/tc-riscv.c: Support the modifier %got_pcrel_hi. * doc/c-riscv.texi: Add documentation. * testsuite/gas/riscv/no-relax-reloc.d: Add test case for the new modifier %got_pcrel_hi. * testsuite/gas/riscv/no-relax-reloc.s: Likewise. * testsuite/gas/riscv/relax-reloc.d: Likewise. * testsuite/gas/riscv/relax-reloc.s: Likewise.