Impact: fix crash with memory hotplug enabled

kernel_physical_mapping_init() is called during memory hotplug
so it does not belong in the init section.

If the kernel is built with CONFIG_DEBUG_SECTION_MISMATCH=y on
the make command line, arch/x86/mm/init_64.c is compiled with
the -fno-inline-functions-called-once gcc option defeating
inlining of kernel_physical_mapping_init() within init_memory_mapping().

When kernel_physical_mapping_init() is not inlined it is placed
in the .init.text section according to the __init in it's current
declaration.  A later call to kernel_physical_mapping_init() during
a memory hotplug operation encounters an int3 trap because the
.init.text section memory has been freed.

This patch eliminates the crash caused by the int3 trap by moving the
non-inlined kernel_physical_mapping_init() from .init.text to .meminit.text.
Signed-off-by: Gary Hade <garyhade@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>