Revert "riscv: Allow use of reset drivers"

This reverts commit 958a3f46.

A more appropriate change below is already in mainline.
Commit fd31e4fd ("riscv: Do not build reset.c if SYSRESET is on")

Revert this patch, so that U-Boot can be built successfully for
SiFive Fu540 board.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Leo Liang <ycliang@andestech.com>