remoteproc: kill IPA notify code

The IPA code now uses the generic remoteproc SSR notification
mechanism.  This makes the original IPA notification code unused
and unnecessary, so get rid of it.

This is effectively a revert of commit d7f5f3c8

 ("remoteproc:
add IPA notification to q6v5 driver").

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20200724181142.13581-3-elder@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>