[AVR32] /sys/kernel/debug/at32ap_clk

When debugfs is available, /sys/kernel/debug/at32ap_clk will provide a
dump of the power manager registers and of the current clock tree.  This
can help sorting out various surprises, and when making runtime PM work.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>