soc: qcom: ipa: AP/modem communications

This patch implements two forms of out-of-band communication between
the AP and modem.

  - QMI is a mechanism that allows clients running on the AP
    interact with services running on the modem (and vice-versa).
    The AP IPA driver uses QMI to communicate with the corresponding
    IPA driver resident on the modem, to agree on parameters used
    with the IPA hardware and to ensure both sides are ready before
    entering operational mode.

  - SMP2P is a more primitive mechanism available for the modem and
    AP to communicate with each other.  It provides a means for either
    the AP or modem to interrupt the other, and furthermore, to provide
    32 bits worth of information.  The IPA driver uses SMP2P to tell
    the modem what the state of the IPA clock was in the event of a
    crash.  This allows the modem to safely access the IPA hardware
    (or avoid doing so) when a crash occurs, for example, to access
    information within the IPA hardware.

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