ARM: OMAP4+: dmm: Take care of overlapping dmm and trap sections.

ARM: OMAP4+: dmm: Take care of overlapping dmm and trap sections.

The DMM sections can be overlapping with each other, with
sections 3 to 0 having the highest to lowest priority in that
order. There could also be a section that is used trap the
unmapped Tiler entries and this trap section could be
overlapping with the actual sdram area.

So take care of the above scenarios while calculating the
size of the actual ram.

Signed-off-by: R Sricharan <r.sricharan@ti.com>