arm: psci: add a weak function psci_arch_cpu_entry

The added function psci_arch_cpu_entry() is called
during psci_cpu_entry() and can be used by arch to handle
PSCI state transition from ON_PENDING to ON.

The default weak function is empty: not behavior change.
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>

arch/arm/cpu/armv7/psci.S

@@ -321,11 +321,18 @@ ENTRY(psci_arch_init)
 ENDPROC(psci_arch_init)
 .weak psci_arch_init
 
+ENTRY(psci_arch_cpu_entry)
+	mov	pc, lr
+ENDPROC(psci_arch_cpu_entry)
+.weak psci_arch_cpu_entry
+
 ENTRY(psci_cpu_entry)
 	bl	psci_enable_smp
 
 	bl	_nonsec_init
 
+	bl	psci_arch_cpu_entry
+
 	bl	psci_get_cpu_id			@ CPU ID => r0
 	mov	r2, r0				@ CPU ID => r2
 	bl	psci_get_context_id		@ context id => r0