Since system controller now has control over SoC power management, it
needs to be explicitly requested to reboot the SoC. Add support for
it.

In some systems however, SoC needs to toggle a GPIO or send event to an
external entity (like a PMIC) for a system reboot to take place. To
facilitate that, we allow for a DT property to determine if the reboot
handler will be registered and further, the service is also made
available to other drivers (such as PMIC driver) to sequence the
additional operation and trigger the SoC reboot as the last step.

Tested-by: Lokesh Vutla <redacted>
Signed-off-by: Nishanth Menon <nm@ti.com>
---
 .../devicetree/bindings/arm/keystone/ti,sci.txt    |  1 +
 drivers/firmware/ti_sci.c                          | 85 ++++++++++++++++++++++
 drivers/firmware/ti_sci.h                          | 12 +++
 include/linux/soc/ti/ti_sci_protocol.h             | 11 +++
 4 files changed, 109 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/keystone/ti,sci.txt b/Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
index 965d45e313b1..ed5b8fc185f1 100644
--- a/Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
+++ b/Documentation/devicetree/bindings/arm/keystone/ti,sci.txt

@@ -38,6 +38,7 @@ Optional Properties:
 - reg-names:
 	debug_messages - Map the Debug message region
 - reg:  register space corresponding to the debug_messages
+- ti,system-reboot-controller: If system reboot can be triggered by SoC reboot