greybus: arche-platform: Power-off unipro subsystem upon suspend

Switch off APBs/SVC/Switch in the suspend call notifier. Note that
this is an interim solution to enable fishfooding.

Testing done:
 - Passed QA sanity test on EVT1.5
 - Suspend current measured at ~70mW

Signed-off-by: David Lin <dtwlin@google.com>
Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
[vaibhav.hiremath@linaro.org: Updated commit description]
Tested-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>