src/dts/Makefile: add install

Create an install option to put PRU dt firmware into /lib/firmware
setup.sh: fix path to kernel module
src/pru-firmware/Makefile: add install command
src/userspace_lib/client.py: changed output pin

The Bacon Cape has an LED tied to P9_42, so using PRU0_4 as the output signal
makes it easy to blink an LED as part of the example.
src/pru-firmware/pru0_firmware: deleted

Binary objects like this shouldn't be under source control