Introduce vcpu_reset and refactor arch_cpu_init

Introduce vcpu_reset calling arch_cpu_init and arch_regs_reset.
vcpu_reset is called from main on cold boot or resume from CPU off.
arch_cpu_init gets a cpu and entry point parameter passed to
PSCI resume function.

Change-Id: I809b453c32b418237b7334d13d8e55916d593b09
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/src/main.c b/src/main.c
index 5f30aac..ea3d3b0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -26,10 +26,8 @@
 
 	vcpu->cpu = c;
 
-	arch_cpu_init();
-
 	/* Reset the registers to give a clean start for vCPU. */
-	arch_regs_reset(vcpu);
+	vcpu_reset(vcpu);
 
 	return vcpu;
 }