ARM: OMAP2+: Use omap initcalls

This way the initcalls don't run on other SoCs on multiplatform
kernels. Otherwise we'll get something like this when booting
on vexpress:

omap_hwmod: _ensure_mpu_hwmod_is_setup: MPU initiator hwmod mpu not yet registered
...
WARNING: at arch/arm/mach-omap2/pm.c:82 _init_omap_device+0x74/0x94()
_init_omap_device: could not find omap_hwmod for mpu
...
omap-dma-engine omap-dma-engine: OMAP DMA engine driver
...

Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/hwspinlock.c

@@ -57,4 +57,4 @@ static int __init hwspinlocks_init(void)
 	return retval;
 }
 /* early board code might need to reserve specific hwspinlock instances */
-postcore_initcall(hwspinlocks_init);
+omap_postcore_initcall(hwspinlocks_init);