Split atmega_common code into avr8_common folder. This moves common
avr8 code to be used for all avr8 variants: tiny, mega and xmega.
Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>
Split out Gunar Schorcht's clever approach to provide thread safe malloc for
AVR into a system module and make AVR depend on this. This allows other
platforms to also use this.