riscv: cpu: Beautify the warning message

Add '\n' to the end of the warning message.

Besides, if we enable console record utility,
missing the '\n' causes the console_record_readline
fail to recognize the end of string.

Signed-off-by: Leo Yu-Chi Liang <ycliang@andestech.com>

arch/riscv/cpu/cpu.c

@@ -463,7 +463,7 @@ static void riscv_parse_isa_string(const char *isa)
 		switch (*ext) {
 		case 'x':
 		case 'X':
-			log_warning("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
+			log_warning("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.\n");
 			/*
 			 * To skip an extension, we find its end.
 			 * As multi-letter extensions must be split from other multi-letter