arm/arm64: Make kvm__arch_delete_ram() aarch32/aarch64 specific

Move kvm__arch_delete_ram() into aarch32 and aarch64 specific locations.
The function is kept identical between the two architectures, but adding
KVM SPE support will mean making changes to the aarch64 version of the
function to unlock the guest memory on virtual machine tear down.

No functional change intended.