When a initrd is given we calculate the next free memory position
as:
free_mem = PAGE_ALIGN(initrd_end);
This is wrong when initrd_end exactly falls on a page boundary.
In this case PAGE_ALIGN() does nothing and free_mem becomes
initrd_end and the following bootm_load_devicetree() and thus
booting fails with -ENOMEM.

Fix this by correctly advancing to the next free memory position.

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