RISC-V: compress "addi d,CV,z" to "c.mv d,CV"

PR 27732
gas/
	* testsuite/gas/riscv/c-zero-imm.d: Compress addi a4,a4,0 to
	c.mv a4,a4.
	* testsuite/gas/riscv/c-zero-imm.s: Likewise.
opcodes/
	* riscv-opc.c (riscv_opcodes): New insn alias for addi. Compress
	"addi d,CV,z" to "c.mv d,CV".

gas/testsuite/gas/riscv/c-zero-imm.d

@@ -12,12 +12,12 @@ Disassembly of section .text:
 [ 	]+4:[ 	]+8a01[ 	]+andi[ 	]+a2,a2,0
 [ 	]+6:[ 	]+8a81[ 	]+andi[ 	]+a3,a3,0
 [ 	]+8:[ 	]+0001[ 	]+nop
-[ 	]+a:[ 	]+00070713[ 	]+mv[ 	]+a4,a4
-[ 	]+e:[ 	]+0781[ 	]+addi[ 	]+a5,a5,0
-[ 	]+10:[ 	]+00051513[ 	]+slli[ 	]+a0,a0,0x0
-[ 	]+14:[ 	]+0005d593[ 	]+srli[ 	]+a1,a1,0x0
-[ 	]+18:[ 	]+40065613[ 	]+srai[ 	]+a2,a2,0x0
-[ 	]+1c:[ 	]+0682[ 	]+c.slli64[ 	]+a3
-[ 	]+1e:[ 	]+8301[ 	]+c.srli64[ 	]+a4
-[ 	]+20:[ 	]+8781[ 	]+c.srai64[ 	]+a5
+[ 	]+a:[ 	]+873a[ 	]+mv[ 	]+a4,a4
+[ 	]+c:[ 	]+0781[ 	]+addi[ 	]+a5,a5,0
+[ 	]+e:[ 	]+00051513[ 	]+slli[ 	]+a0,a0,0x0
+[ 	]+12:[ 	]+0005d593[ 	]+srli[ 	]+a1,a1,0x0
+[ 	]+16:[ 	]+40065613[ 	]+srai[ 	]+a2,a2,0x0
+[ 	]+1a:[ 	]+0682[ 	]+c.slli64[ 	]+a3
+[ 	]+1c:[ 	]+8301[ 	]+c.srli64[ 	]+a4
+[ 	]+1e:[ 	]+8781[ 	]+c.srai64[ 	]+a5
 #...

gas/testsuite/gas/riscv/c-zero-imm.s

@@ -5,7 +5,7 @@
 	andi a2,a2,0
 	c.andi a3,0
 	addi x0,x0,0
-	# Don't let this compress to a hint.
+	# compress to c.mv.
 	addi a4,a4,0
 	# These are hints.
 	c.addi a5,0

opcodes/riscv-opc.c

@@ -276,6 +276,7 @@ const struct riscv_opcode riscv_opcodes[] =
 {"addi",        0, INSN_CLASS_C, "d,CU,z",    MATCH_C_NOP, MASK_C_ADDI|MASK_RVC_IMM, match_c_nop, INSN_ALIAS },
 {"addi",        0, INSN_CLASS_C, "Cc,Cc,CL",  MATCH_C_ADDI16SP, MASK_C_ADDI16SP, match_c_addi16sp, INSN_ALIAS },
 {"addi",        0, INSN_CLASS_C, "d,Cz,Co",   MATCH_C_LI, MASK_C_LI, match_rd_nonzero, INSN_ALIAS },
+{"addi",        0, INSN_CLASS_C, "d,CV,z",      MATCH_C_MV, MASK_C_MV, match_c_add, INSN_ALIAS },
 {"addi",        0, INSN_CLASS_I, "d,s,j",     MATCH_ADDI, MASK_ADDI, match_opcode, 0 },
 {"add",         0, INSN_CLASS_C, "d,CU,CV",   MATCH_C_ADD, MASK_C_ADD, match_c_add, INSN_ALIAS },
 {"add",         0, INSN_CLASS_C, "d,CV,CU",   MATCH_C_ADD, MASK_C_ADD, match_c_add, INSN_ALIAS },