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

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

Instead of setting the CPU psci-conduit and start-powered-off
properties in the 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 or to the generic loader.  (EL3 guest code started
via -bios or -pflash was already being run with PSCI emulation
disabled.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Tested-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20220127154639.2090164-9-peter.maydell@linaro.org