vmm/linux/tee: Handle KVM_EXIT_HYPERCALL exits

SEV-SNP guests use KVM_EXIT_HYPERCALL exits to signal to the hypervisor
it would like some pages set to private or shared.

Implements a handler that manages guest memory and can set regions to
private or shared. vCPUs can send "memory properties" messages
to the handler indicating:

- Guest GPA
- Size of memory region
- Whether the region should be set to private or shared

The handler will read these messages and configure the memory regions
accordingly.

Signed-off-by: Tyler Fanelli <[email protected]>

Author: tylerfanelli