omap_save_bootinfo derefences the argument passed to barebox without
checking it for validity. This breaks 2nd stage booting where r0
is undefined. The best we can do is to check whether the pointer is
somewhere in SRAM and is word aligned. This at least makes sure that
we do not oops. This introduces SoC specific xxx_save_bootinfo variants
since the SRAM addresses/sizes differ between SoCs.

Additionally fix the prototype for omap_save_bootinfo. It uses r0, so
it must be passed this variable.

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