soc: qcom: ipa: immediate commands

One TX endpoint (per EE) is used for issuing immediate commands to
the IPA.  These commands request activites beyond simple data
transfers to be done by the IPA hardware.  For example, the IPA is
able to manage routing packets among endpoints, and immediate commands
are used to configure tables used for that routing.

Immediate commands are built on top of GSI transactions.  They are
different from normal transfers (in that they use a special endpoint,
and their "payload" is interpreted differently), so separate functions
are used to issue immediate command transactions.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>