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>
diff --git a/arch/arm/mach-omap2/pmu.c b/arch/arm/mach-omap2/pmu.c
index eb78ae7..75052b3 100644
--- a/arch/arm/mach-omap2/pmu.c
+++ b/arch/arm/mach-omap2/pmu.c
@@ -89,4 +89,4 @@
 
 	return omap2_init_pmu(oh_num, oh_names);
 }
-subsys_initcall(omap_init_pmu);
+omap_subsys_initcall(omap_init_pmu);