Declare some structure types in a few header files where functions
declared therein use them:
  - Functions are declared in "gsi_private.h" that use gsi, gsi_ring, and
    gsi_trans structure pointers.
  - A gsi_trans struct pointer is passed to two functions
    declared in "ipa_endpoint.h"
  - In "ipa_interrupt.h", a platform_device pointer is passed in the
    declaration for ipa_interrupt_init().
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>