AVR32: Resource management rewrite

AVR32: Resource management rewrite

Rewrite the resource management code (i.e. I/O memory, clock gating,
gpio) so it doesn't depend on any global state. This is necessary
because this code is heavily used before relocation to RAM, so we
can't write to any global variables.

As an added bonus, this makes u-boot's memory footprint a bit smaller,
although some functionality has been left out; all clocks are enabled
all the time, and there's no checking for gpio line conflicts.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>