fix(intel): update boot scratch to indicate to Uboot is PSCI ON

fix(intel): update boot scratch to indicate to Uboot is PSCI ON

There is a use case where kernel requested ATF to power off/on only CPU0.
However, after ATF power off/on CPU0, CPU0 did not back into the state
to wait for ATF. Instead, CPU0 continue to reentry SPL boot sequence
because CPU0 is master/primary core. This causing the system reboot from
SPL again, while the slave core still in kernel.

To resolve this, ATF is set the boot scratch register 8 bit 17 whenever
it is a request from kernel to power off/on only CPU0. So, if this boot
scratch bit is set, CPU 0 will be able to put into a state to wait for
ATF.

Signed-off-by: Jit Loon Lim <jit.loon.lim@intel.com>
Change-Id: Ia0228c5396beaa479858f5bd02fc05139efd2423