[BUILD] conditionally compile common/cmd_*.c in common/Makefile

Modify common/Makefile to conditionally compile the cmd_*.c files based
on the board config.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

common/cmd_i2c.c

@@ -86,9 +86,6 @@
 #include <i2c.h>
 #include <asm/byteorder.h>
 
-#if defined(CONFIG_CMD_I2C)
-
-
 /* Display values from last command.
  * Memory modify remembered values are different from display memory.
  */
@@ -1024,5 +1021,3 @@ U_BOOT_CMD(
 	"      (valid chip values 50..57)\n"
 );
 #endif
-
-#endif