modprobe domain was allowed to launch vendor toolbox even if its a
coredomain. That violates the treble separation. Fix that by creating a
separate 'vendor_modprobe' domain that init is allowed to transition to
through vendor_toolbox.

Bug: 37008075
Test: Build and boot sailfish

Change-Id: Ic3331797691bb5d1fdc05a674aa4aa313e1f86b2
Signed-off-by: Sandeep Patil <sspatil@google.com>