Discover device base addresses from the DTB

The base addresses of various components can differ from one model to
another. As these addresses are currently hard-coded in the bootwrapper,
it is necessary to manually alter the bootwrapper for each variation.

This patch adds scripting to extract the (absolute / CPU) addresses of
various system components. With this change the bootwrapper build system
will automatically discover the addresses that need to be used.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>