[IA64] kexec: declare ia64_mca_pal_base in mca.h rather than kexec.h

* Kexec adds some code to arch/ia64/kernel/smp.c which needs ia64_mca_pal_base,
  so the kexec patch (actually the kdump patch) declares this
  per-cpu variable in include/asm-ia64/kexec.h.

* ia64_mca_pal_base is defined in arch/ia64/kernel/mca.c, so it
  seems to me that it would make a lot more sense to declare it in
  include/asm-ia64/mca.h.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Tony Luck <tony.luck@intel.com>