hw/arm/versal: Let boot.c handle PSCI enablement

Instead of setting the CPU psci-conduit and start-powered-off
properties in the xlnx-versal-virt board code, set the arm_boot_info
psci_conduit field so that the boot.c code can do it.

This will fix a corner case where we were incorrectly enabling PSCI
emulation when booting guest code into EL3 because it was an ELF file
passed to -kernel.  (EL3 guest code started via -bios, -pflash, or
the generic loader was already being run with PSCI emulation
disabled.)

Note that EL3 guest code has no way to turn on the secondary CPUs
because there's no emulated power controller, but this was already
true for EL3 guest code run via -bios, -pflash, or the generic
loader.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Tested-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Tested-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20220127154639.2090164-8-peter.maydell@linaro.org