ANDROID: KVM: arm64: Support multiple FF-A partition buffers

Remove the host buffers and keep an array of buffers which will be used
by different FF-A partitions identified by the vm handle. Limit the
array size to the maximum number of supported PVMs.

Bug: 269285339
Bug: 278749606
Change-Id: Ie5aee49b25268f5c79de2f0aca5fbe88755a4ddf
Signed-off-by: Sebastian Ene <sebastianene@google.com>