[U-Boot] [BUG] simple-bus and rsa-sw with DM_FLAG_PRE_RELOC

[AKASHI Takahiro]

As of v2019.07-rc1,
u-boot does fail to boot without any messages on qemu-arm64 when
configured with qemu_arm64_defconfig plus CONFIG_RSA/RSA_SOFTWARE_EXP.
(Note that RSA_SOFTWARE_EXP also declares itself with DM_FLAG_PRE_RELOC.)

By bisecting between v2019.04 and v2019.07, I found that the following
commit triggered this regression:

        commit 3a7c45f6a772
        Author: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
        Date:   Wed Apr 10 14:46:07 2019 +0200

            simple-bus: add DM_FLAG_PRE_RELOC flag to simple-bus driver

What's wrong with this?

-Takahiro Akashi