tlkd: execute standard SMC calls on the boot CPU

This patch checks if standard SMC calls, meant for TLK, are issued
only on the boot CPU. TLK is UP Trusted OS stack and so we need this
check to avoid the NS world calling into TLK from any other CPU.

The previous check tied TLK to CPU0, but the boot CPU can be other
than CPU0 in some scenarios.

Change-Id: I75eaafa32471ce19e9920433c2f97b6b5fc02d86
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>