remoteproc: Drop wait in __rproc_boot()

In the event that rproc_boot() is called before the firmware loaded
completion has been flagged it will wait with the mutex held,
obstructing the request_firmware_nowait() callback from completing the
wait.

As rproc_fw_config_virtio() has been reduced to only triggering
auto-boot there is no longer a reason for waiting in rproc_boot(), so
drop this.

Cc: Sarangdhar Joshi <spjoshi@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>