ANDROID: KVM: arm64: Don't prepopulate MMIO regions for host stage-2

As we reserve only 1GB of memory for the MMIO region don't prepopulate
the entire remaining address space with MMIO as this is prone to failure.
Instead, let the MMIO regions to be created lazily on the fault path and
keep only the RAM regions prepopulated.

Bug: 307805059
Test: Boot pKVM with CONFIG_ARM64_16K_PAGES
Change-Id: I6327f42eb17c6588335a1e04736393c9032114ab
Signed-off-by: Sebastian Ene <sebastianene@google.com>