OMAP4: Pandaboard: Add omap_reserve functionality

This patch adds omap_reserve functionality to board-omap4panda.c.
Helps in the reserving boot time memory in SDRAM, used here for
framebuffer allocation.

This patch is in similar lines to commit id 71ee7dad, from
Russell king

Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Raghuveer Murthy <raghuveer.murthy@ti.com>
[tony@atomide.com: fixed to be before .map_io as pointed out by Russell King]
Signed-off-by: Tony Lindgren <tony@atomide.com>