forked from Mirrors/opensbi

For some debuggers that do not implement SYSWRITEC and SYSREADC operations, we can use SYSWRITE and SYSREAD instead like the implementation of semihosting_getc(). Signed-off-by: Chen Pei <cp0613@linux.alibaba.com> Reviewed-by: Xiang W <wxjstz@126.com> Reviewed-by: Anup Patel <anup@brainfault.org>