ARM: omap: fix section mismatch warning for omap_secondary_startup()

WARNING: vmlinux.o(.text+0x1c664): Section mismatch in reference from the function omap_secondary_startup() to the function .cpuinit.text:secondary_startup()
The function omap_secondary_startup() references
the function __cpuinit secondary_startup().
This is often because omap_secondary_startup lacks a __cpuinit
annotation or the annotation of secondary_startup is wrong.

Unfortunately, fixing this causes a new warning which is harder to
solve:

WARNING: arch/arm/mach-omap2/built-in.o(.text+0x5328): Section mismatch in reference from the function omap4_hotplug_cpu() to the function .cpuinit.text:omap_secondary_startup()
The function omap4_hotplug_cpu() references
the function __cpuinit omap_secondary_startup().
This is often because omap4_hotplug_cpu lacks a __cpuinit
annotation or the annotation of omap_secondary_startup is wrong.

because omap4_hotplug_cpu() is used by power management code as well,
which may not end up using omap_secondary_startup().

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>