ANDROID: KVM: arm64: Specify stage-2-protected regions in DT

Parse the devicetree during pKVM init to find nodes with the
"pkvm,protected-region" compatible string. These nodes specify a
physical address range in reg that must alway be mapped as invalid in
the host stage-2 page table when running under pKVM.

Example DT:

        pkvm_prot_reg: pkvm_prot_reg@80000000 {
                compatible = "pkvm,protected-region";
                reg = <0x00 0x80000000 0x00 0x200000>;
        };

Bug: 244543039
Bug: 244373730
Change-Id: I102cd16c91d96e5283cdd1a4fa58836cc4834eac
Signed-off-by: Quentin Perret <qperret@google.com>