arm: smh: Add some functions for working with the host console

This adds three wrappers around the semihosting commands for reading and
writing to the host console. We use the more standard getc/putc/puts
names instead of readc/writec/write0 for familiarity.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>

include/semihosting.h

@@ -86,4 +86,23 @@ long smh_flen(long fd);
  */
 long smh_seek(long fd, long pos);
 
+/**
+ * smh_getc() - Read a character from stdin
+ *
+ * Return: The character read, or a negative error on failure
+ */
+int smh_getc(void);
+
+/**
+ * smh_putc() - Print a character on stdout
+ * @ch: The character to print
+ */
+void smh_putc(char ch);
+
+/**
+ * smh_write0() - Print a nul-terminated string on stdout
+ * @s: The string to print
+ */
+void smh_puts(const char *s);
+
 #endif /* _SEMIHOSTING_H */