[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_ext2.c

@@ -34,8 +34,6 @@
  */
 #include <common.h>
 #include <part.h>
-
-#if defined(CONFIG_CMD_EXT2)
 #include <config.h>
 #include <command.h>
 #include <image.h>
@@ -259,5 +257,3 @@ U_BOOT_CMD(
 	"    - load binary file 'filename' from 'dev' on 'interface'\n"
 	"      to address 'addr' from ext2 filesystem\n"
 );
-
-#endif