i2ccmds: Pass the i2c address as a 7-bit number (0-127)

The sam3 i2c code and the linux code use a 7-bit i2c address, while
the avr, lpc176x, and samd21 i2c code uses an 8-bit address with the
least significant bit always zero.  A similar issue occurred in the
host code (sx1509.py and replicape.py use 7-bit addresses while
uc1701.py and mcp4451.py use 8-bit addresses).

Consistently use 7-bit addresses in all the code.  This breaks
compatibility between host and mcu software, so make a change to the
config_i2c command to force users to synchronize software updates.
This also breaks common Smoothieboard configs, so update the mcp4451
code to validate the i2c_address.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/lpc176x/i2c.c

@@ -45,7 +45,7 @@ i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
     if (bus)
         shutdown("Unsupported i2c bus");
     i2c_init();
-    return (struct i2c_config){ .addr=addr };
+    return (struct i2c_config){ .addr=addr<<1 };
 }
 
 static void