arm: psci: save context id for cpu_on PSCI command

Save and use the 3rd parameter of PSCI CPU_ON request: context_id.

The context_id parameter is only meaningful to the caller.
U-Boot PSCI preserves a copy of the value passed in this parameter.
Following wakeup from a  powerdown state, U-BOOT PSCI places
this value in R0 when it first enters the OS.

NB: this context id is not (yet?) used by Linux but it is mandatory
    to be PSCI compliant.

update armv7 psci functions:
- psci_save_target_pc(): keep for backward compatibility with
  current platform (only save PC and force context id to 0)
  => should be removed when all platform migrate to the new API

- psci_save(): new API to use by ARMv7 platform with PSCI,
  save pc (= entry_point_address) and context_id

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/cpu/armv7/psci.S b/arch/arm/cpu/armv7/psci.S
index 95b962d..35fd955 100644
--- a/arch/arm/cpu/armv7/psci.S
+++ b/arch/arm/cpu/armv7/psci.S
@@ -327,6 +327,10 @@
 	bl	_nonsec_init
 
 	bl	psci_get_cpu_id			@ CPU ID => r0
+	mov	r2, r0				@ CPU ID => r2
+	bl	psci_get_context_id		@ context id => r0
+	mov	r1, r0				@ context id => r1
+	mov	r0, r2				@ CPU ID => r0
 	bl	psci_get_target_pc		@ target PC => r0
 	b	_do_nonsec_entry
 ENDPROC(psci_cpu_entry)