Kernel Driver: Add idx parameter to pru_start

For future use, single-PRU firmware

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net>
[pru_rproc] Cleanups to ready for patching

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net>
Kernel Driver: Assorted Cleanups & Fixes

TODO:
 * Implement write overrun checks
 * Device tree parameter reads

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net>