Fixes amremote_config installation if target dir does not exist.

In my custom builds I remove build gdb debugger and server for target. This has the side affect of the $(TARGET_DIR)/usr/bin not existing yet during the installation step of the amremote_config.  This caused keytest to be lost and amremote_config command to be moved as a normal file of the name bin to $(TARGET_DIR)/usr.

This change fixes the installation step to use install to create $(TARGET_DIR)/usr/bin.  In addition, I changed the other install commands to explicitly use the install -t form which would error out, instead of making a normal file called bin.