vmm: Add Debuggable trait implementation

This commit adds initial gdb.rs implementation for `Debuggable` trait to
describe a debuggable component. Some part of the trait bound
implementations is based on the crosvm GDB stub code [1].

[1] https://github.com/google/crosvm/blob/main/src/gdb.rs

Signed-off-by: Akira Moroo <retrage01@gmail.com>

vmm/Cargo.toml

@@ -9,6 +9,7 @@ default = []
 acpi = ["acpi_tables","devices/acpi", "arch/acpi"]
 cmos = ["devices/cmos"]
 fwdebug = ["devices/fwdebug"]
+gdb = ["kvm"]
 kvm = ["hypervisor/kvm", "vfio-ioctls/kvm", "vm-device/kvm", "pci/kvm"]
 mshv = ["hypervisor/mshv", "virtio-devices/mshv", "vfio-ioctls/mshv", "vm-device/mshv", "pci/mshv"]
 tdx = ["arch/tdx", "hypervisor/tdx"]
@@ -24,6 +25,8 @@ clap = "3.1.1"
 devices = { path = "../devices" }
 epoll = "4.3.1"
 event_monitor = { path = "../event_monitor" }
+gdbstub = "0.6.0"
+gdbstub_arch = "0.2.0"
 hypervisor = { path = "../hypervisor" }
 lazy_static = "1.4.0"
 libc = "0.2.119"