x86: compile error fix for smpboot.c

Without this patch, my link fails with:

arch/x86/kernel/built-in.o(.cpuinit.text+0x3c6e): In function `get_local_pda':
: undefined reference to `_cpu_pda'
arch/x86/kernel/built-in.o(.cpuinit.text+0x3cd1): In function `get_local_pda':
: undefined reference to `after_bootmem'
arch/x86/kernel/built-in.o(.cpuinit.text+0x3cec): In function `get_local_pda':
: undefined reference to `_cpu_pda'
make[2]: *** [.tmp_vmlinux1] Error 1

Caused by commit 766da892634694f795b18b9538407816896fc470
    x86: remove static boot_cpu_pda array v2

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>