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: NSean Anderson <sean.anderson@seco.com>

arch/arm/lib/semihosting.c

@@ -15,8 +15,11 @@
 
 #define SYSOPEN		0x01
 #define SYSCLOSE	0x02
+#define SYSWRITEC	0x03
+#define SYSWRITE0	0x04
 #define SYSWRITE	0x05
 #define SYSREAD		0x06
+#define SYSREADC	0x07
 #define SYSSEEK		0x0A
 #define SYSFLEN		0x0C
 #define SYSERRNO	0x13
@@ -167,3 +170,18 @@ long smh_seek(long fd, long pos)
 		return smh_errno();
 	return 0;
 }
+
+int smh_getc(void)
+{
+	return smh_trap(SYSREADC, NULL);
+}
+
+void smh_putc(char ch)
+{
+	smh_trap(SYSWRITEC, &ch);
+}
+
+void smh_puts(const char *s)
+{
+	smh_trap(SYSWRITE0, (char *)s);
+}

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 */