arch: Move mpspec to arch crate and simplify

Remove unnecessary code for these structs. Moving this also allows the
removal of the arch_gen crate.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

Cargo.lock

@@ -62,7 +62,6 @@ version = "0.1.0"
 dependencies = [
  "acpi_tables",
  "anyhow",
- "arch_gen",
  "byteorder",
  "hypervisor",
  "libc",
@@ -76,10 +75,6 @@ dependencies = [
  "vm-migration",
 ]
 
-[[package]]
-name = "arch_gen"
-version = "0.1.0"
-
 [[package]]
 name = "atty"
 version = "0.2.14"