efi_loader: Fix configuration table override

Before commit 7cbc1241 ("efi_loader: initalize EFI object list
only once") we recreated the world on every bootefi invocation.

That included the object tree as well as the configuration tables.

Now however we don't recreate them, which means we must not explicitly
override the configuration tables, as otherwise we may lose our SMBIOS
table from the configuration table list on second bootefi invocation.

This patch makes bootefi call our normal configuration table modification
APIs to add/remove the FDT instead of recreating all tables from scratch.
That way the SMBIOS table gets preserved across multiple invocations.

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