efi_loader: Disable env_save() call on boot

With the introduction of EFI variable support, we also wanted to persist
these EFI variables. However, the way it was implemented we ended up
persisting all U-Boot environment variables on every EFI boot.

That could potentially lead to unexpected side effects because variables
that were not supposed to be written to persisted env get written. It also
means we may end up writing the environment more often than we should.

For this release, let's just disable EFI variable persistence and instead
implement it properly for the next one.

Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Fixes: ad644e7c ("efi_loader: efi variable support")
Signed-off-by: Alexander Graf <agraf@suse.de>
Acked-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>