efi: Work around ia64 build problem with ESRT driver

So, I'm told this problem exists in the world:

 > Subject: Build error in -next due to 'efi: Add esrt support'
 >
 > Building ia64:defconfig ... failed
 > --------------
 > Error log:
 >
 > drivers/firmware/efi/esrt.c:28:31: fatal error: asm/early_ioremap.h: No such file or directory
 >

I'm not really sure how it's okay that we have things in asm-generic on
some platforms but not others - is having it the same everywhere not the
whole point of asm-generic?

That said, ia64 doesn't have early_ioremap.h .  So instead, since it's
difficult to imagine new IA64 machines with UEFI 2.5, just don't build
this code there.

To me this looks like a workaround - doing something like:

generic-y += early_ioremap.h

in arch/ia64/include/asm/Kbuild would appear to be more correct, but
ia64 has its own early_memremap() decl in arch/ia64/include/asm/io.h ,
and it's a macro.  So adding the above /and/ requiring that asm/io.h be
included /after/ asm/early_ioremap.h in all cases would fix it, but
that's pretty ugly as well.  Since I'm not going to spend the rest of my
life rectifying ia64 headers vs "generic" headers that aren't generic,
it's much simpler to just not build there.

Note that I've only actually tried to build this patch on x86_64, but
esrt.o still gets built there, and that would seem to demonstrate that
the conditional building is working correctly at all the places the code
built before.  I no longer have any ia64 machines handy to test that the
exclusion actually works there.

Signed-off-by: Peter Jones <pjones@redhat.com>
Acked-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
(Compile-)Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>