cbufp: fix unit test compile error
vas_mgr: refactor expand function
valloc: refactor valloc_free() to be less ugly.
valloc: fix code that worked by coincidence
cbufp: new interface functions map_at and unmap_at

map_at is meant to support mapping a cbufp's memory buffer
directly into another component's VAS. unmap_at deletes the
mapping. Unit tests are added in unit_cbuf1 and unit_cbufp.
vas_mgr: add vas_mgr_take() function
valloc: add valloc_alloc_at()