arm: mach-k3: am642: Shut down R5 core after ATF startup on A53

The AM642 SoCs use the Main R5FSS0 as a boot processor, and runs
the R5 SPL that performs the initialization of the System Controller
processor and starting the Arm Trusted Firmware (ATF) on the Arm
Cortex A53 cluster. The Core0 serves as this boot processor and is
parked in WFE after all the initialization. Core1 does not directly
participate in the boot flow, and is simply parked in a WFI.

Power down these R5 cores (and the associated RTI timer resources
that were indirectly powered up) after starting up ATF on A53 by
using the appropriate SYSFW API in release_resources_for_core_shutdown().
This allows these Main R5F cores to be further controlled from the
A53 to run regular applications.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>