sconfig: Add 10bit addressing mode to i2c device type

Use the second token for an i2c device entry in devicetree.cb to
indicate if it should use 10-bit addressing or 7-bit.  The default if
not provided is to use 7-bit addressing, but it can be changed to
10-bit addressing with the ".1" suffix.  For example:

chip drivers/i2c/generic
  device i2c 3a.1 on end
end

Change-Id: I1d81a7e154fbc040def4d99ad07966fac242a472
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/14788
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/device/path.h

@@ -53,6 +53,7 @@ struct pnp_path
 struct i2c_path
 {
 	unsigned device;
+	unsigned mode_10bit;
 };
 
 struct apic_path