x86/headers: Remove APIC headers from <asm/smp.h>

The APIC headers are relatively complex and bring in additional
header dependencies - while smp.h is a relatively simple header
included from high level headers.

Remove the dependency and add in the missing #include's in .c
files where they gained it indirectly before.

Signed-off-by: Ingo Molnar <mingo@kernel.org>