The memory calculations used are all hardcoded into three different
files, start-pbl.c, uncompress.c and start.c. To make this more readable
and reliable, this patch gathers these information in barebox-arm.h with
static inline functions for the calculation of the memory offsets.

This patch also adds proper handling of different barebox/board data
sizes. Currently only 1MB+Alignment of RAM is reserved for Barebox and
board data. This could be too small for bigger devicetrees and barebox.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>