plat/arm: remove weak implemention of 'plat_arm_psci_override_pm_ops' function

In order to allow Arm platforms to override the default list of PSCI
callbacks, remove the existing weak implementation of
'plat_arm_psci_override_pm_ops' function and let all the Arm platforms
implement their own 'plat_arm_psci_override_pm_ops' function.

For platforms that support SCMI protocol, the function
'css_scmi_override_pm_ops' can be additionally used as well to
override the default PSCI callbacks.

Change-Id: If7c27468bd51a00ea9c2a3716b5894163f5a9f3c
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
diff --git a/plat/arm/css/sgm/sgm_bl31_setup.c b/plat/arm/css/sgm/sgm_bl31_setup.c
index 29c32e7..952572e 100644
--- a/plat/arm/css/sgm/sgm_bl31_setup.c
+++ b/plat/arm/css/sgm/sgm_bl31_setup.c
@@ -47,3 +47,8 @@
 
 	arm_bl31_early_platform_setup((void *)arg0, arg1, arg2, (void *)arg3);
 }
+
+const plat_psci_ops_t *plat_arm_psci_override_pm_ops(plat_psci_ops_t *ops)
+{
+	return css_scmi_override_pm_ops(ops);
+}