avr32: Clean up HMATRIX code

Introduce a few helper functions for HMATRIX configuration and clean up
the register definitions. Also add definitions for the HMATRIX master
and slave IDs on the AT32AP700x chips.

Also make the definitions in hmatrix.h available to board code by moving
it to <mach/hmatrix.h>

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