hw/misc/sifive_u_otp: Use IF_PFLASH for the OTP device instead of IF_NONE

hw/misc/sifive_u_otp: Use IF_PFLASH for the OTP device instead of IF_NONE

Configuring a drive with "if=none" is meant for creation of a backend
only, it should not get automatically assigned to a device frontend.
Use "if=pflash" for the One-Time-Programmable device instead (like
it is e.g. also done for the efuse device in hw/arm/xlnx-zcu102.c).

Since the old way of configuring the device has already been published
with the previous QEMU versions, we cannot remove this immediately, but
have to deprecate it and support it for at least two more releases.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20211119102549.217755-1-thuth@redhat.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>