opcodes/
* riscv-opc.c (match_c_add_with_hint, match_c_lui_with_hint): New.
(riscv_opcodes) <li>: Delete "d,0" line. Change Cj to Co.
<andi, and, add, addiw, addw, c.addi>: Change Cj to Co.
<add>: Add explanatory comment for 4-operand add instruction.
<c.nop>: Add support for immediate operand.
<c.mv, c.add>: Use match_c_add_with_hint instead of match_c_add.
<c.lui>: Use match_c_lui_with_hint instead of match_c_lui.
<c.li, c.slli>: Use match_opcode instead of match_rd_nonzero.