efi_loader: Allow SMBIOS tables in highmem

We try hard to make sure that SMBIOS tables live in the lower 32bit.
However, when we can not find any space at all there, we should not
error out but instead just fall back to map them in the full address
space instead.

This can for example happen on systems that do not have any RAM mapped
in the lower 32bits of address space. In that case having any SMBIOS
tables at all is better than having none.

Signed-off-by: Alexander Graf <agraf@suse.de>