ANDROID: KVM: arm64: Expose __pkvm_create_private_mapping to pKVM modules

pKVM has an internal API allowing to create mappings in the 'private'
range of the hypervisor VA space for which there are no rules
constraining the VA-PA relation (hence comparable to the vmalloc area in
the kernel). This will be a useful API for hypervisor modules, so expose
it in the recently introduced module ops struct.

Bug: 278749606
Bug: 244543039
Bug: 244373730
Change-Id: I2a8f958a02c3c3b9871224b65b00b207820a507a
Signed-off-by: Quentin Perret <qperret@google.com>