accel/ivpu: Fix power down sequence

Remove FPGA workaround on power_down to skip checking for noc
quiescent state.

Put VPU in reset before powering it down and skip manipulating
registers that are reset by the VPU reset.

This fixes power down errors where VPU is powered down just after VPU
is booted.

Fixes: 35b13763

 ("accel/ivpu: Introduce a new DRM driver for Intel VPU")
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323125504.2586442-5-stanislaw.gruszka@linux.intel.com