vbox_x86: have separate system and data disks

The boot, recovery, and system partitions are now mounted from /dev/sda, while
userdata and cache are mounted from /dev/sdb.  To this end, we have two new
build targets, in addition to android_disk_vdi:

    make android_system_disk_vdi will build /dev/sda
    make android_user_disk_vdi will build /dev/sdb

android_disk_vdi will build both disks.

Change-Id: I7389194429d42eca4800c5bb41d32099b7eeafa1
Signed-off-by: Iliyan Malchev <malchev@google.com>
4 files changed