avr: Add an extra shortcut for useful gcc size opt.

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
lib: Fix compilation issues with printk & panic

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
rf24: Fix race condition in rf24_write, cleanups

There was a race condition in rf24_write that resulted
in ack payload lost. This commit hopefully fixes it.

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
rf24: Implement agressive size optimisation hack

For AVR RF-bootloader, since we want that in 4K

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>