[IA64] dmi.h: Make dmi_alloc use kzalloc

x86/ia64 have a slight mismatch in dmi_alloc as
x86 does a memset(0), and ia64 just does kmalloc.

Make the ia64 dmi_alloc match the x86 style.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>