Add AVR hardware support.

This patch adds an avrdude configuration and procedures for using energytool.
See the board files for examples of how to use them.

	* dejagnu/baseboards/atmega328p-shrimp.exp: New board file for the
	shrimp.
	* dejagnu/baseboards/atxmega256a3bu.exp: New board file for the
	atxmega256a3bu Xplained board.
	* dejagnu/config/avrdude.exp: Main configuration for using avrdude to
	flash a program and then measure it.
	* dejagnu/config/energytool.exp: Extra procedures for spawning and
	loggind energytool.
	* site.exp: Add dejagnu/config to the search directories.