[PATCH] qemu-riscv64_smode, sifive-fu540: fix extlinux (define preboot)

[PATCH] qemu-riscv64_smode, sifive-fu540: fix extlinux (define preboot)

From 3fc056f0b9f7c26e58a1e947c8c0184e55919614 Mon Sep 17 00:00:00 2001
Forwarded: https://patchwork.ozlabs.org/patch/1151125/

Commit 37304aaf60bf92a5dc3ef222ba520698bd862a44 removed preboot
commands in RISC-V targets and broke extlinux support as reported
by Fu Wei <wefu@redhat.com>.

The patch finishes migration of CONFIG_USE_PREBOOT and CONFIG_REBOOT
to Kconfig.

Signed-off-by: David Abdurachmanov <david.abdurachmanov@sifive.com>
Gbp-Pq: Topic riscv64
Gbp-Pq: Name qemu-riscv64_smode-sifive-fu540-fix-extlinux-define-.patch