omap_reserve() callback is defned only for mach-omap2.
So, moving definition of omap_reserve() to mach-omap2.
This helps is moving plat/omap_secure.h local to
mach-omap2
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com> Signed-off-by: Tony Lindgren <tony@atomide.com>