ARM: OMAP2+: Round of the carve out memory requested to section_size

memblock_steal tries to reserve physical memory during boot.
When the requested size is not aligned on the section size
then, the remaining memory available for lowmem becomes
unaligned on the section boundary. There is a issue with this,
which is discussed in the thread below.

https://lkml.org/lkml/2012/6/28/112

The final conclusion from the thread seems to
be align the memblock_steal calls on the SECTION boundary.
The issue comes out when LPAE is enabled, where the
section size is 2MB.

Boot tested this on OMAP5 evm with and without LPAE.

Signed-off-by: R Sricharan <r.sricharan@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>