feat(cros-kernel/x86_64): add XEN domu support

delete the CONFIG_XEN options from the kernel and add the domu features
that are listed on the wiki:

http://wiki.xen.org/wiki/Mainline_Linux_Kernel_Configs

sdk_container/src/third_party/coreos-overlay/eclass/cros-kernel/x86_64_defconfig

@@ -478,40 +478,22 @@ CONFIG_LIBCRC32C=m
 # CONFIG_XZ_DEC_ARM is not set
 # CONFIG_XZ_DEC_ARMTHUMB is not set
 # CONFIG_XZ_DEC_SPARC is not set
+CONFIG_PARAVIRT=y
 CONFIG_XEN=y
-CONFIG_XEN_DOM0=y
+CONFIG_PARAVIRT_GUEST=y
-CONFIG_XEN_PRIVILEGED_GUEST=y
+CONFIG_PARAVIRT_SPINLOCKS=y
-CONFIG_XEN_PVHVM=y
+CONFIG_HVC_DRIVER=y
-CONFIG_XEN_MAX_DOMAIN_MEMORY=500
-CONFIG_XEN_SAVE_RESTORE=y
-CONFIG_XEN_DEBUG_FS=y
-CONFIG_PCI_XEN=y
-CONFIG_XEN_PCIDEV_FRONTEND=m
-CONFIG_XEN_BLKDEV_FRONTEND=m
-CONFIG_XEN_BLKDEV_BACKEND=m
-CONFIG_NETXEN_NIC=m
-CONFIG_XEN_NETDEV_FRONTEND=m
-CONFIG_XEN_NETDEV_BACKEND=m
-CONFIG_INPUT_XEN_KBDDEV_FRONTEND=y
 CONFIG_HVC_XEN=y
-CONFIG_HVC_XEN_FRONTEND=y
-CONFIG_XEN_WDT=m
 CONFIG_XEN_FBDEV_FRONTEND=y
-CONFIG_XEN_BALLOON=y
+CONFIG_XEN_BLKDEV_FRONTEND=y
-CONFIG_XEN_SELFBALLOONING=y
+CONFIG_XEN_NETDEV_FRONTEND=y
-CONFIG_XEN_SCRUB_PAGES=y
+CONFIG_XEN_PCIDEV_FRONTEND=y
-CONFIG_XEN_DEV_EVTCHN=m
+CONFIG_INPUT_XEN_KBDDEV_FRONTEND=y
-CONFIG_XEN_BACKEND=y
+CONFIG_XEN_FBDEV_FRONTEND=y
-CONFIG_XENFS=m
-CONFIG_XEN_COMPAT_XENFS=y
-CONFIG_XEN_SYS_HYPERVISOR=y
 CONFIG_XEN_XENBUS_FRONTEND=y
-CONFIG_XEN_GNTDEV=m
+CONFIG_XEN_SAVE_RESTORE=y
 CONFIG_XEN_GRANT_DEV_ALLOC=m
-CONFIG_SWIOTLB_XEN=y
 CONFIG_XEN_TMEM=y
-CONFIG_XEN_PCIDEV_BACKEND=m
+CONFIG_CLEANCACHE=y
-CONFIG_XEN_PRIVCMD=m
+CONFIG_FRONTSWAP=y
-CONFIG_XEN_ACPI_PROCESSOR=m
+CONFIG_XEN_SELFBALLOONING=y
-# CONFIG_XEN_MCE_LOG is not set
-CONFIG_XEN_HAVE_PVMMU=y